diff --git a/composer.lock b/composer.lock
index b908faaf7c..2c36f66299 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4474,12 +4474,12 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/phpstan/phpstan-strict-rules.git",
-                "reference": "6c7a9815bb3af49113a6f85d073e3e2fc01f7ffa"
+                "reference": "a9b2cb1ee2668ac3a66b5f76f37122e64299c2ca"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/phpstan/phpstan-strict-rules/zipball/6c7a9815bb3af49113a6f85d073e3e2fc01f7ffa",
-                "reference": "6c7a9815bb3af49113a6f85d073e3e2fc01f7ffa",
+                "url": "https://api.github.com/repos/phpstan/phpstan-strict-rules/zipball/a9b2cb1ee2668ac3a66b5f76f37122e64299c2ca",
+                "reference": "a9b2cb1ee2668ac3a66b5f76f37122e64299c2ca",
                 "shasum": ""
             },
             "require": {
@@ -4518,7 +4518,7 @@
                 "issues": "https://github.com/phpstan/phpstan-strict-rules/issues",
                 "source": "https://github.com/phpstan/phpstan-strict-rules/tree/master"
             },
-            "time": "2021-09-22T16:41:47+00:00"
+            "time": "2021-09-23T08:29:12+00:00"
         },
         {
             "name": "phpunit/php-code-coverage",
diff --git a/src/Analyser/FileAnalyser.php b/src/Analyser/FileAnalyser.php
index af21ba3f71..c13f5429b3 100644
--- a/src/Analyser/FileAnalyser.php
+++ b/src/Analyser/FileAnalyser.php
@@ -108,7 +108,7 @@ public function analyseFile(
 							$metadata = [];
 							if ($scope->isInTrait()) {
 								$traitReflection = $scope->getTraitReflection();
-								if ($traitReflection->getFileName() !== false) {
+								if ($traitReflection->getFileName() !== null) {
 									$traitFilePath = $traitReflection->getFileName();
 								}
 							}
diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index be1d52b3f9..395b8126dd 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -292,7 +292,7 @@ public function getFileDescription(): string
 		}
 
 		$traitReflection = $this->context->getTraitReflection();
-		if ($traitReflection->getFileName() === false) {
+		if ($traitReflection->getFileName() === null) {
 			throw new \PHPStan\ShouldNotHappenException();
 		}
 
@@ -2588,7 +2588,7 @@ private function resolveExactName(Name $name): ?string
 					return null;
 				}
 				$currentClassReflection = $this->getClassReflection();
-				if ($currentClassReflection->getParentClass() !== false) {
+				if ($currentClassReflection->getParentClass() !== null) {
 					return $currentClassReflection->getParentClass()->getName();
 				}
 				return null;
@@ -2614,7 +2614,7 @@ public function resolveName(Name $name): string
 				return $this->getClassReflection()->getName();
 			} elseif ($originalClass === 'parent') {
 				$currentClassReflection = $this->getClassReflection();
-				if ($currentClassReflection->getParentClass() !== false) {
+				if ($currentClassReflection->getParentClass() !== null) {
 					return $currentClassReflection->getParentClass()->getName();
 				}
 			}
@@ -3385,7 +3385,7 @@ public function getFunctionType($type, bool $isNullable, bool $isVariadic): Type
 			$className = (string) $type;
 			$lowercasedClassName = strtolower($className);
 			if ($lowercasedClassName === 'parent') {
-				if ($this->isInClass() && $this->getClassReflection()->getParentClass() !== false) {
+				if ($this->isInClass() && $this->getClassReflection()->getParentClass() !== null) {
 					return new ObjectType($this->getClassReflection()->getParentClass()->getName());
 				}
 
diff --git a/src/Analyser/NodeScopeResolver.php b/src/Analyser/NodeScopeResolver.php
index 5e3e16c307..cbde3f80ee 100644
--- a/src/Analyser/NodeScopeResolver.php
+++ b/src/Analyser/NodeScopeResolver.php
@@ -3663,7 +3663,7 @@ private function processTraitUse(Node\Stmt\TraitUse $node, MutatingScope $classS
 			}
 			$traitReflection = $this->reflectionProvider->getClass($traitName);
 			$traitFileName = $traitReflection->getFileName();
-			if ($traitFileName === false) {
+			if ($traitFileName === null) {
 				continue; // trait from eval or from PHP itself
 			}
 			$fileName = $this->fileHelper->normalizePath($traitFileName);
diff --git a/src/Analyser/ResultCache/ResultCacheManager.php b/src/Analyser/ResultCache/ResultCacheManager.php
index 71ae46d78c..46b2205628 100644
--- a/src/Analyser/ResultCache/ResultCacheManager.php
+++ b/src/Analyser/ResultCache/ResultCacheManager.php
@@ -633,7 +633,7 @@ private function getProjectExtensionFiles(?array $projectConfig, array $dependen
 
 					$classReflection = $this->reflectionProvider->getClass($class);
 					$fileName = $classReflection->getFileName();
-					if ($fileName === false) {
+					if ($fileName === null) {
 						continue;
 					}
 
diff --git a/src/Analyser/TypeSpecifier.php b/src/Analyser/TypeSpecifier.php
index fbf31d29f4..5a6453374b 100644
--- a/src/Analyser/TypeSpecifier.php
+++ b/src/Analyser/TypeSpecifier.php
@@ -123,7 +123,7 @@ public function specifyTypesInCondition(
 				} elseif ($lowercasedClassName === 'parent') {
 					if (
 						$scope->isInClass()
-						&& $scope->getClassReflection()->getParentClass() !== false
+						&& $scope->getClassReflection()->getParentClass() !== null
 					) {
 						$type = new ObjectType($scope->getClassReflection()->getParentClass()->getName());
 					} else {
diff --git a/src/Dependency/DependencyResolver.php b/src/Dependency/DependencyResolver.php
index 3580e529cd..5507705a72 100644
--- a/src/Dependency/DependencyResolver.php
+++ b/src/Dependency/DependencyResolver.php
@@ -230,7 +230,7 @@ private function addClassToDependencies(string $className, array &$dependenciesR
 			}
 
 			$classReflection = $classReflection->getParentClass();
-		} while ($classReflection !== false);
+		} while ($classReflection !== null);
 	}
 
 	private function getFunctionReflection(\PhpParser\Node\Name $nameNode, ?Scope $scope): ReflectionWithFilename
diff --git a/src/Dependency/NodeDependencies.php b/src/Dependency/NodeDependencies.php
index cd75370e7d..b6fcb0ce51 100644
--- a/src/Dependency/NodeDependencies.php
+++ b/src/Dependency/NodeDependencies.php
@@ -41,7 +41,7 @@ public function getFileDependencies(string $currentFile, array $analysedFiles):
 
 		foreach ($this->reflections as $dependencyReflection) {
 			$dependencyFile = $dependencyReflection->getFileName();
-			if ($dependencyFile === false) {
+			if ($dependencyFile === null) {
 				continue;
 			}
 			$dependencyFile = $this->fileHelper->normalizePath($dependencyFile);
diff --git a/src/PhpDoc/PhpDocBlock.php b/src/PhpDoc/PhpDocBlock.php
index 92fa123c71..3127628d9f 100644
--- a/src/PhpDoc/PhpDocBlock.php
+++ b/src/PhpDoc/PhpDocBlock.php
@@ -341,7 +341,7 @@ private static function getParentReflections(ClassReflection $classReflection):
 		$result = [];
 
 		$parent = $classReflection->getParentClass();
-		if ($parent !== false) {
+		if ($parent !== null) {
 			$result[] = $parent;
 		}
 
diff --git a/src/PhpDoc/TypeNodeResolver.php b/src/PhpDoc/TypeNodeResolver.php
index 10c701a90a..39ac549568 100644
--- a/src/PhpDoc/TypeNodeResolver.php
+++ b/src/PhpDoc/TypeNodeResolver.php
@@ -310,7 +310,7 @@ private function resolveIdentifierTypeNode(IdentifierTypeNode $typeNode, NameSco
 				case 'parent':
 					if ($this->getReflectionProvider()->hasClass($nameScope->getClassName())) {
 						$classReflection = $this->getReflectionProvider()->getClass($nameScope->getClassName());
-						if ($classReflection->getParentClass() !== false) {
+						if ($classReflection->getParentClass() !== null) {
 							return new ObjectType($classReflection->getParentClass()->getName());
 						}
 					}
@@ -681,7 +681,7 @@ private function resolveConstTypeNode(ConstTypeNode $typeNode, NameScope $nameSc
 					case 'parent':
 						if ($this->getReflectionProvider()->hasClass($nameScope->getClassName())) {
 							$classReflection = $this->getReflectionProvider()->getClass($nameScope->getClassName());
-							if ($classReflection->getParentClass() === false) {
+							if ($classReflection->getParentClass() === null) {
 								return new ErrorType();
 
 							}
diff --git a/src/Reflection/BetterReflection/BetterReflectionProvider.php b/src/Reflection/BetterReflection/BetterReflectionProvider.php
index 850eb36364..f26041e01a 100644
--- a/src/Reflection/BetterReflection/BetterReflectionProvider.php
+++ b/src/Reflection/BetterReflection/BetterReflectionProvider.php
@@ -210,7 +210,7 @@ public function getAnonymousClassReflection(\PhpParser\Node\Stmt\Class_ $classNo
 			$scopeFile = $scope->getFile();
 		} else {
 			$scopeFile = $scope->getTraitReflection()->getFileName();
-			if ($scopeFile === false) {
+			if ($scopeFile === null) {
 				$scopeFile = $scope->getFile();
 			}
 		}
@@ -297,9 +297,8 @@ private function getCustomFunction(string $functionName): \PHPStan\Reflection\Ph
 			return $parameter->getName();
 		}, $reflectionFunction->getParameters()));
 		if ($resolvedPhpDoc === null && $reflectionFunction->getFileName() !== false && $reflectionFunction->getDocComment() !== false) {
-			$fileName = $reflectionFunction->getFileName();
 			$docComment = $reflectionFunction->getDocComment();
-			$resolvedPhpDoc = $this->fileTypeMapper->getResolvedPhpDoc($fileName, null, null, $reflectionFunction->getName(), $docComment);
+			$resolvedPhpDoc = $this->fileTypeMapper->getResolvedPhpDoc($reflectionFunction->getFileName(), null, null, $reflectionFunction->getName(), $docComment);
 		}
 
 		if ($resolvedPhpDoc !== null) {
@@ -326,7 +325,7 @@ private function getCustomFunction(string $functionName): \PHPStan\Reflection\Ph
 			$isDeprecated,
 			$isInternal,
 			$isFinal,
-			$reflectionFunction->getFileName(),
+			$reflectionFunction->getFileName() !== false ? $reflectionFunction->getFileName() : null,
 			$isPure
 		);
 	}
diff --git a/src/Reflection/ClassConstantReflection.php b/src/Reflection/ClassConstantReflection.php
index 88f87bf8f7..a89d59d7cc 100644
--- a/src/Reflection/ClassConstantReflection.php
+++ b/src/Reflection/ClassConstantReflection.php
@@ -53,12 +53,7 @@ public function getName(): string
 
 	public function getFileName(): ?string
 	{
-		$fileName = $this->declaringClass->getFileName();
-		if ($fileName === false) {
-			return null;
-		}
-
-		return $fileName;
+		return $this->declaringClass->getFileName();
 	}
 
 	/**
diff --git a/src/Reflection/ClassReflection.php b/src/Reflection/ClassReflection.php
index eee291e8a7..80b1cb4c09 100644
--- a/src/Reflection/ClassReflection.php
+++ b/src/Reflection/ClassReflection.php
@@ -97,16 +97,16 @@ class ClassReflection implements ReflectionWithFilename
 	private array $subclasses = [];
 
 	/** @var string|false|null */
-	private $filename;
+	private $filename = false;
 
 	/** @var string|false|null */
-	private $reflectionDocComment;
+	private $reflectionDocComment = false;
 
 	/** @var \PHPStan\Reflection\ClassReflection[]|null */
 	private ?array $cachedInterfaces = null;
 
 	/** @var \PHPStan\Reflection\ClassReflection|false|null */
-	private $cachedParentClass = null;
+	private $cachedParentClass = false;
 
 	/** @var array<string, TypeAlias>|null */
 	private ?array $typeAliases = null;
@@ -161,12 +161,9 @@ public function getNativeReflection(): \ReflectionClass
 		return $this->reflection;
 	}
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName()
+	public function getFileName(): ?string
 	{
-		if (isset($this->filename)) {
+		if ($this->filename !== false) {
 			return $this->filename;
 		}
 
@@ -175,11 +172,11 @@ public function getFileName()
 		}
 		$fileName = $this->reflection->getFileName();
 		if ($fileName === false) {
-			return $this->filename = false;
+			return $this->filename = null;
 		}
 
 		if (!file_exists($fileName)) {
-			return $this->filename = false;
+			return $this->filename = null;
 		}
 
 		return $this->filename = $fileName;
@@ -191,27 +188,19 @@ public function getFileNameWithPhpDocs(): ?string
 			return $this->stubPhpDocBlock->getFilename();
 		}
 
-		$filename = $this->getFileName();
-		if ($filename === false) {
-			return null;
-		}
-
-		return $filename;
+		return $this->getFileName();
 	}
 
-	/**
-	 * @return false|\PHPStan\Reflection\ClassReflection
-	 */
-	public function getParentClass()
+	public function getParentClass(): ?ClassReflection
 	{
-		if ($this->cachedParentClass !== null) {
+		if ($this->cachedParentClass !== false) {
 			return $this->cachedParentClass;
 		}
 
 		$parentClass = $this->reflection->getParentClass();
 
 		if ($parentClass === false) {
-			return $this->cachedParentClass = false;
+			return $this->cachedParentClass = null;
 		}
 
 		$extendsTag = $this->getFirstExtendsTag();
@@ -575,7 +564,7 @@ public function getParents(): array
 	{
 		$parents = [];
 		$parent = $this->getParentClass();
-		while ($parent !== false) {
+		while ($parent !== null) {
 			$parents[] = $parent;
 			$parent = $parent->getParentClass();
 		}
@@ -595,7 +584,7 @@ public function getInterfaces(): array
 		$interfaces = $this->getImmediateInterfaces();
 		$immediateInterfaces = $interfaces;
 		$parent = $this->getParentClass();
-		while ($parent !== false) {
+		while ($parent !== null) {
 			foreach ($parent->getImmediateInterfaces() as $parentInterface) {
 				$interfaces[$parentInterface->getName()] = $parentInterface;
 				foreach ($this->collectInterfaces($parentInterface) as $parentInterfaceInterface) {
@@ -640,7 +629,7 @@ public function getImmediateInterfaces(): array
 	{
 		$indirectInterfaceNames = [];
 		$parent = $this->getParentClass();
-		while ($parent !== false) {
+		while ($parent !== null) {
 			foreach ($parent->getNativeReflection()->getInterfaceNames() as $parentInterfaceName) {
 				$indirectInterfaceNames[] = $parentInterfaceName;
 			}
@@ -740,7 +729,7 @@ public function getParentClassesNames(): array
 	{
 		$parentNames = [];
 		$currentClassReflection = $this;
-		while ($currentClassReflection->getParentClass() !== false) {
+		while ($currentClassReflection->getParentClass() !== null) {
 			$parentNames[] = $currentClassReflection->getParentClass()->getName();
 			$currentClassReflection = $currentClassReflection->getParentClass();
 		}
@@ -780,7 +769,7 @@ public function getConstant(string $name): ConstantReflection
 				$declaringClass->getName(),
 				$name
 			);
-			if ($resolvedPhpDoc === null && $fileName !== false) {
+			if ($resolvedPhpDoc === null && $fileName !== null) {
 				$docComment = null;
 				if ($reflectionConstant->getDocComment() !== false) {
 					$docComment = $reflectionConstant->getDocComment();
@@ -1097,15 +1086,16 @@ public function getResolvedPhpDoc(): ?ResolvedPhpDocBlock
 		}
 
 		$fileName = $this->getFileName();
-		if ($fileName === false) {
+		if ($fileName === null) {
 			return null;
 		}
 
-		if ($this->reflectionDocComment === null) {
-			$this->reflectionDocComment = $this->reflection->getDocComment();
+		if ($this->reflectionDocComment === false) {
+			$docComment = $this->reflection->getDocComment();
+			$this->reflectionDocComment = $docComment !== false ? $docComment : null;
 		}
 
-		if ($this->reflectionDocComment === false) {
+		if ($this->reflectionDocComment === null) {
 			return null;
 		}
 
@@ -1189,7 +1179,7 @@ public function getAncestors(): array
 			}
 
 			$parent = $this->getParentClass();
-			if ($parent !== false) {
+			if ($parent !== null) {
 				$addToAncestors($parent->getName(), $parent);
 				foreach ($parent->getAncestors() as $name => $ancestor) {
 					$addToAncestors($name, $ancestor);
diff --git a/src/Reflection/FunctionReflectionFactory.php b/src/Reflection/FunctionReflectionFactory.php
index caf4d05e72..dccd3a19b0 100644
--- a/src/Reflection/FunctionReflectionFactory.php
+++ b/src/Reflection/FunctionReflectionFactory.php
@@ -19,7 +19,7 @@ interface FunctionReflectionFactory
 	 * @param bool $isDeprecated
 	 * @param bool $isInternal
 	 * @param bool $isFinal
-	 * @param string|false $filename
+	 * @param string|null $filename
 	 * @param bool|null $isPure
 	 * @return PhpFunctionReflection
 	 */
@@ -33,7 +33,7 @@ public function create(
 		bool $isDeprecated,
 		bool $isInternal,
 		bool $isFinal,
-		$filename,
+		?string $filename,
 		?bool $isPure = null
 	): PhpFunctionReflection;
 
diff --git a/src/Reflection/Php/BuiltinMethodReflection.php b/src/Reflection/Php/BuiltinMethodReflection.php
index efc2f4e0b4..266d002075 100644
--- a/src/Reflection/Php/BuiltinMethodReflection.php
+++ b/src/Reflection/Php/BuiltinMethodReflection.php
@@ -11,22 +11,13 @@ public function getName(): string;
 
 	public function getReflection(): ?\ReflectionMethod;
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName();
+	public function getFileName(): ?string;
 
 	public function getDeclaringClass(): \ReflectionClass;
 
-	/**
-	 * @return int|false
-	 */
-	public function getStartLine();
+	public function getStartLine(): ?int;
 
-	/**
-	 * @return int|false
-	 */
-	public function getEndLine();
+	public function getEndLine(): ?int;
 
 	public function getDocComment(): ?string;
 
diff --git a/src/Reflection/Php/FakeBuiltinMethodReflection.php b/src/Reflection/Php/FakeBuiltinMethodReflection.php
index a1737af26c..cfb2d1b831 100644
--- a/src/Reflection/Php/FakeBuiltinMethodReflection.php
+++ b/src/Reflection/Php/FakeBuiltinMethodReflection.php
@@ -30,12 +30,9 @@ public function getReflection(): ?\ReflectionMethod
 		return null;
 	}
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName()
+	public function getFileName(): ?string
 	{
-		return false;
+		return null;
 	}
 
 	public function getDeclaringClass(): \ReflectionClass
@@ -43,20 +40,14 @@ public function getDeclaringClass(): \ReflectionClass
 		return $this->declaringClass;
 	}
 
-	/**
-	 * @return int|false
-	 */
-	public function getStartLine()
+	public function getStartLine(): ?int
 	{
-		return false;
+		return null;
 	}
 
-	/**
-	 * @return int|false
-	 */
-	public function getEndLine()
+	public function getEndLine(): ?int
 	{
-		return false;
+		return null;
 	}
 
 	public function getDocComment(): ?string
diff --git a/src/Reflection/Php/NativeBuiltinMethodReflection.php b/src/Reflection/Php/NativeBuiltinMethodReflection.php
index 8a59bb0237..692c06a010 100644
--- a/src/Reflection/Php/NativeBuiltinMethodReflection.php
+++ b/src/Reflection/Php/NativeBuiltinMethodReflection.php
@@ -24,12 +24,14 @@ public function getReflection(): ?\ReflectionMethod
 		return $this->reflection;
 	}
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName()
+	public function getFileName(): ?string
 	{
-		return $this->reflection->getFileName();
+		$fileName = $this->reflection->getFileName();
+		if ($fileName === false) {
+			return null;
+		}
+
+		return $fileName;
 	}
 
 	public function getDeclaringClass(): \ReflectionClass
@@ -37,20 +39,24 @@ public function getDeclaringClass(): \ReflectionClass
 		return $this->reflection->getDeclaringClass();
 	}
 
-	/**
-	 * @return int|false
-	 */
-	public function getStartLine()
+	public function getStartLine(): ?int
 	{
-		return $this->reflection->getStartLine();
+		$line = $this->reflection->getStartLine();
+		if ($line === false) {
+			return null;
+		}
+
+		return $line;
 	}
 
-	/**
-	 * @return int|false
-	 */
-	public function getEndLine()
+	public function getEndLine(): ?int
 	{
-		return $this->reflection->getEndLine();
+		$line = $this->reflection->getEndLine();
+		if ($line === false) {
+			return null;
+		}
+
+		return $line;
 	}
 
 	public function getDocComment(): ?string
diff --git a/src/Reflection/Php/PhpClassReflectionExtension.php b/src/Reflection/Php/PhpClassReflectionExtension.php
index 223476e4c6..0692f245c4 100644
--- a/src/Reflection/Php/PhpClassReflectionExtension.php
+++ b/src/Reflection/Php/PhpClassReflectionExtension.php
@@ -219,7 +219,7 @@ private function createProperty(
 		);
 		$stubPhpDocString = null;
 		if ($resolvedPhpDoc === null) {
-			if ($declaringClassReflection->getFileName() !== false) {
+			if ($declaringClassReflection->getFileName() !== null) {
 				$declaringTraitName = $this->findPropertyTrait($propertyReflection);
 				$constructorName = null;
 				if (method_exists($propertyReflection, 'isPromoted') && $propertyReflection->isPromoted()) {
@@ -262,7 +262,7 @@ private function createProperty(
 		}
 
 		if ($phpDocType === null) {
-			if (isset($constructorName) && $declaringClassReflection->getFileName() !== false) {
+			if (isset($constructorName) && $declaringClassReflection->getFileName() !== null) {
 				$constructorDocComment = $declaringClassReflection->getConstructor()->getDocComment();
 				$nativeClassReflection = $declaringClassReflection->getNativeReflection();
 				$positionalParameterNames = [];
@@ -302,7 +302,7 @@ private function createProperty(
 		if (
 			$phpDocType === null
 			&& $this->inferPrivatePropertyTypeFromConstructor
-			&& $declaringClassReflection->getFileName() !== false
+			&& $declaringClassReflection->getFileName() !== null
 			&& $propertyReflection->isPrivate()
 			&& (!method_exists($propertyReflection, 'hasType') || !$propertyReflection->hasType())
 			&& $declaringClassReflection->hasConstructor()
@@ -578,7 +578,7 @@ private function createMethod(
 		$stubPhpDocString = null;
 
 		if ($resolvedPhpDoc === null) {
-			if ($declaringClass->getFileName() !== false) {
+			if ($declaringClass->getFileName() !== null) {
 				$docComment = $methodReflection->getDocComment();
 				$positionalParameterNames = array_map(static function (\ReflectionParameter $parameter): string {
 					return $parameter->getName();
@@ -618,7 +618,7 @@ private function createMethod(
 		if (
 			$methodReflection instanceof NativeBuiltinMethodReflection
 			&& $methodReflection->isConstructor()
-			&& $declaringClass->getFileName() !== false
+			&& $declaringClass->getFileName() !== null
 		) {
 			foreach ($methodReflection->getParameters() as $parameter) {
 				if (!method_exists($parameter, 'isPromoted') || !$parameter->isPromoted()) {
@@ -923,7 +923,7 @@ private function inferAndCachePropertyTypes(
 		if (isset($this->propertyTypesCache[$declaringClass->getName()])) {
 			return $this->propertyTypesCache[$declaringClass->getName()];
 		}
-		if ($declaringClass->getFileName() === false) {
+		if ($declaringClass->getFileName() === null) {
 			return $this->propertyTypesCache[$declaringClass->getName()] = [];
 		}
 
diff --git a/src/Reflection/Php/PhpFunctionReflection.php b/src/Reflection/Php/PhpFunctionReflection.php
index f16327cfd5..3193522627 100644
--- a/src/Reflection/Php/PhpFunctionReflection.php
+++ b/src/Reflection/Php/PhpFunctionReflection.php
@@ -49,8 +49,7 @@ class PhpFunctionReflection implements FunctionReflection, ReflectionWithFilenam
 
 	private bool $isFinal;
 
-	/** @var string|false */
-	private $filename;
+	private ?string $filename;
 
 	private ?bool $isPure;
 
@@ -70,7 +69,7 @@ class PhpFunctionReflection implements FunctionReflection, ReflectionWithFilenam
 	 * @param bool $isDeprecated
 	 * @param bool $isInternal
 	 * @param bool $isFinal
-	 * @param string|false $filename
+	 * @param string|null $filename
 	 * @param bool|null $isPure
 	 */
 	public function __construct(
@@ -86,7 +85,7 @@ public function __construct(
 		bool $isDeprecated,
 		bool $isInternal,
 		bool $isFinal,
-		$filename,
+		?string $filename,
 		?bool $isPure = null
 	)
 	{
@@ -111,17 +110,14 @@ public function getName(): string
 		return $this->reflection->getName();
 	}
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName()
+	public function getFileName(): ?string
 	{
-		if ($this->filename === false) {
-			return false;
+		if ($this->filename === null) {
+			return null;
 		}
 
 		if (!file_exists($this->filename)) {
-			return false;
+			return null;
 		}
 
 		return $this->filename;
diff --git a/src/Reflection/Php/PhpMethodReflection.php b/src/Reflection/Php/PhpMethodReflection.php
index c6fab4535e..50cbd8d81a 100644
--- a/src/Reflection/Php/PhpMethodReflection.php
+++ b/src/Reflection/Php/PhpMethodReflection.php
@@ -268,7 +268,7 @@ private function isVariadic(): bool
 			$filename = $this->declaringTrait->getFileName();
 		}
 
-		if (!$isNativelyVariadic && $filename !== false && file_exists($filename)) {
+		if (!$isNativelyVariadic && $filename !== null && file_exists($filename)) {
 			$modifiedTime = filemtime($filename);
 			if ($modifiedTime === false) {
 				$modifiedTime = time();
diff --git a/src/Reflection/ReflectionWithFilename.php b/src/Reflection/ReflectionWithFilename.php
index 5bedac9600..c626dbb7cf 100644
--- a/src/Reflection/ReflectionWithFilename.php
+++ b/src/Reflection/ReflectionWithFilename.php
@@ -6,9 +6,6 @@
 interface ReflectionWithFilename
 {
 
-	/**
-	 * @return string|false
-	 */
-	public function getFileName();
+	public function getFileName(): ?string;
 
 }
diff --git a/src/Reflection/Runtime/RuntimeReflectionProvider.php b/src/Reflection/Runtime/RuntimeReflectionProvider.php
index 9e5a5bc98a..daf6fa24f9 100644
--- a/src/Reflection/Runtime/RuntimeReflectionProvider.php
+++ b/src/Reflection/Runtime/RuntimeReflectionProvider.php
@@ -308,7 +308,7 @@ private function getCustomFunction(\PhpParser\Node\Name $nameNode, ?Scope $scope
 			$isDeprecated,
 			$isInternal,
 			$isFinal,
-			$reflectionFunction->getFileName(),
+			$reflectionFunction->getFileName() !== false ? $reflectionFunction->getFileName() : null,
 			$isPure
 		);
 		$this->customFunctionReflections[$lowerCasedFunctionName] = $functionReflection;
diff --git a/src/Rules/Classes/ClassConstantRule.php b/src/Rules/Classes/ClassConstantRule.php
index 4ab9d2e083..58d5b8e65e 100644
--- a/src/Rules/Classes/ClassConstantRule.php
+++ b/src/Rules/Classes/ClassConstantRule.php
@@ -78,7 +78,7 @@ public function processNode(Node $node, Scope $scope): array
 					];
 				}
 				$currentClassReflection = $scope->getClassReflection();
-				if ($currentClassReflection->getParentClass() === false) {
+				if ($currentClassReflection->getParentClass() === null) {
 					return [
 						RuleErrorBuilder::message(sprintf(
 							'Access to parent::%s but %s does not extend any class.',
diff --git a/src/Rules/Classes/InstantiationRule.php b/src/Rules/Classes/InstantiationRule.php
index 71d4b62949..94237c0b6d 100644
--- a/src/Rules/Classes/InstantiationRule.php
+++ b/src/Rules/Classes/InstantiationRule.php
@@ -103,7 +103,7 @@ private function checkClassName(string $class, bool $isName, Node $node, Scope $
 					RuleErrorBuilder::message(sprintf('Using %s outside of class scope.', $class))->build(),
 				];
 			}
-			if ($scope->getClassReflection()->getParentClass() === false) {
+			if ($scope->getClassReflection()->getParentClass() === null) {
 				return [
 					RuleErrorBuilder::message(sprintf(
 						'%s::%s() calls new parent but %s does not extend any class.',
diff --git a/src/Rules/Constants/OverridingConstantRule.php b/src/Rules/Constants/OverridingConstantRule.php
index 336d42d69c..34f9bf424e 100644
--- a/src/Rules/Constants/OverridingConstantRule.php
+++ b/src/Rules/Constants/OverridingConstantRule.php
@@ -131,7 +131,7 @@ private function findPrototype(ClassReflection $classReflection, string $constan
 		}
 
 		$parentClass = $classReflection->getParentClass();
-		if ($parentClass === false) {
+		if ($parentClass === null) {
 			return null;
 		}
 
diff --git a/src/Rules/Generics/CrossCheckInterfacesHelper.php b/src/Rules/Generics/CrossCheckInterfacesHelper.php
index 4bc11186c4..65f5e8d86f 100644
--- a/src/Rules/Generics/CrossCheckInterfacesHelper.php
+++ b/src/Rules/Generics/CrossCheckInterfacesHelper.php
@@ -52,7 +52,7 @@ public function check(ClassReflection $classReflection): array
 
 			$parent = $classReflection->getParentClass();
 			$checkParents = true;
-			if ($first && $parent !== false) {
+			if ($first && $parent !== null) {
 				$extendsTags = $classReflection->getExtendsTags();
 				if (!array_key_exists($parent->getName(), $extendsTags)) {
 					$checkParents = false;
@@ -60,7 +60,7 @@ public function check(ClassReflection $classReflection): array
 			}
 
 			if ($checkParents) {
-				while ($parent !== false) {
+				while ($parent !== null) {
 					$check($parent, false);
 					$parent = $parent->getParentClass();
 				}
diff --git a/src/Rules/Methods/CallMethodsRule.php b/src/Rules/Methods/CallMethodsRule.php
index 8007179b40..d04d600986 100644
--- a/src/Rules/Methods/CallMethodsRule.php
+++ b/src/Rules/Methods/CallMethodsRule.php
@@ -99,7 +99,7 @@ static function (Type $type) use ($name): bool {
 				$referencedClass = $directClassNames[0];
 				$methodClassReflection = $this->reflectionProvider->getClass($referencedClass);
 				$parentClassReflection = $methodClassReflection->getParentClass();
-				while ($parentClassReflection !== false) {
+				while ($parentClassReflection !== null) {
 					if ($parentClassReflection->hasMethod($name)) {
 						return [
 							RuleErrorBuilder::message(sprintf(
diff --git a/src/Rules/Methods/CallStaticMethodsRule.php b/src/Rules/Methods/CallStaticMethodsRule.php
index cdef6c8fdf..87fda9718c 100644
--- a/src/Rules/Methods/CallStaticMethodsRule.php
+++ b/src/Rules/Methods/CallStaticMethodsRule.php
@@ -103,7 +103,7 @@ public function processNode(Node $node, Scope $scope): array
 					];
 				}
 				$currentClassReflection = $scope->getClassReflection();
-				if ($currentClassReflection->getParentClass() === false) {
+				if ($currentClassReflection->getParentClass() === null) {
 					return [
 						RuleErrorBuilder::message(sprintf(
 							'%s::%s() calls parent::%s() but %s does not extend any class.',
diff --git a/src/Rules/Methods/MethodSignatureRule.php b/src/Rules/Methods/MethodSignatureRule.php
index 2599c46ea2..080aa2d58d 100644
--- a/src/Rules/Methods/MethodSignatureRule.php
+++ b/src/Rules/Methods/MethodSignatureRule.php
@@ -129,7 +129,7 @@ private function collectParentMethods(string $methodName, ClassReflection $class
 		$parentMethods = [];
 
 		$parentClass = $class->getParentClass();
-		if ($parentClass !== false && $parentClass->hasNativeMethod($methodName)) {
+		if ($parentClass !== null && $parentClass->hasNativeMethod($methodName)) {
 			$parentMethod = $parentClass->getNativeMethod($methodName);
 			if (!$parentMethod->isPrivate()) {
 				$parentMethods[] = $parentMethod;
diff --git a/src/Rules/Methods/OverridingMethodRule.php b/src/Rules/Methods/OverridingMethodRule.php
index 059c21df82..56cdd11762 100644
--- a/src/Rules/Methods/OverridingMethodRule.php
+++ b/src/Rules/Methods/OverridingMethodRule.php
@@ -62,7 +62,7 @@ public function processNode(Node $node, Scope $scope): array
 		if ($prototype->getDeclaringClass()->getName() === $method->getDeclaringClass()->getName()) {
 			if (strtolower($method->getName()) === '__construct') {
 				$parent = $method->getDeclaringClass()->getParentClass();
-				if ($parent !== false && $parent->hasConstructor()) {
+				if ($parent !== null && $parent->hasConstructor()) {
 					$parentConstructor = $parent->getConstructor();
 					if ($parentConstructor->isFinal()->yes()) {
 						return $this->addErrors([
diff --git a/src/Rules/Properties/AccessPropertiesRule.php b/src/Rules/Properties/AccessPropertiesRule.php
index 6de912f2fe..c2d43fab36 100644
--- a/src/Rules/Properties/AccessPropertiesRule.php
+++ b/src/Rules/Properties/AccessPropertiesRule.php
@@ -123,7 +123,7 @@ static function (Type $type) use ($name): bool {
 				$referencedClass = $typeResult->getReferencedClasses()[0];
 				$propertyClassReflection = $this->reflectionProvider->getClass($referencedClass);
 				$parentClassReflection = $propertyClassReflection->getParentClass();
-				while ($parentClassReflection !== false) {
+				while ($parentClassReflection !== null) {
 					if ($parentClassReflection->hasProperty($name)) {
 						return [
 							RuleErrorBuilder::message(sprintf(
diff --git a/src/Rules/Properties/AccessStaticPropertiesRule.php b/src/Rules/Properties/AccessStaticPropertiesRule.php
index b29beb813b..7d96f249f3 100644
--- a/src/Rules/Properties/AccessStaticPropertiesRule.php
+++ b/src/Rules/Properties/AccessStaticPropertiesRule.php
@@ -101,7 +101,7 @@ private function processSingleProperty(Scope $scope, StaticPropertyFetch $node,
 						))->build(),
 					];
 				}
-				if ($scope->getClassReflection()->getParentClass() === false) {
+				if ($scope->getClassReflection()->getParentClass() === null) {
 					return [
 						RuleErrorBuilder::message(sprintf(
 							'%s::%s() accesses parent::$%s but %s does not extend any class.',
diff --git a/src/Rules/Properties/OverridingPropertyRule.php b/src/Rules/Properties/OverridingPropertyRule.php
index 9f5bc22434..ad45a22d52 100644
--- a/src/Rules/Properties/OverridingPropertyRule.php
+++ b/src/Rules/Properties/OverridingPropertyRule.php
@@ -208,7 +208,7 @@ public function processNode(Node $node, Scope $scope): array
 	private function findPrototype(ClassReflection $classReflection, string $propertyName): ?PhpPropertyReflection
 	{
 		$parentClass = $classReflection->getParentClass();
-		if ($parentClass === false) {
+		if ($parentClass === null) {
 			return null;
 		}
 
diff --git a/src/Type/FileTypeMapper.php b/src/Type/FileTypeMapper.php
index d9b14ab7a3..85344d851f 100644
--- a/src/Type/FileTypeMapper.php
+++ b/src/Type/FileTypeMapper.php
@@ -462,7 +462,7 @@ function (\PhpParser\Node $node) use ($fileName, $lookForTrait, $traitMethodAlia
 						if (!$traitReflection->isTrait()) {
 							continue;
 						}
-						if ($traitReflection->getFileName() === false) {
+						if ($traitReflection->getFileName() === null) {
 							continue;
 						}
 						if (!file_exists($traitReflection->getFileName())) {
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index 2214826e94..846cf7960a 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -527,7 +527,7 @@ public function toArray(): Type
 			}
 
 			$classReflection = $classReflection->getParentClass();
-		} while ($classReflection !== false);
+		} while ($classReflection !== null);
 
 		return new ConstantArrayType($arrayKeys, $arrayValues);
 	}
@@ -1092,7 +1092,7 @@ private function getParent(): ?ObjectType
 		}
 
 		$parentReflection = $thisReflection->getParentClass();
-		if ($parentReflection === false) {
+		if ($parentReflection === null) {
 			return null;
 		}
 
diff --git a/src/Type/ParserNodeTypeToPHPStanType.php b/src/Type/ParserNodeTypeToPHPStanType.php
index c337f65221..4ed5f5b10a 100644
--- a/src/Type/ParserNodeTypeToPHPStanType.php
+++ b/src/Type/ParserNodeTypeToPHPStanType.php
@@ -31,7 +31,7 @@ public static function resolve($type, ?ClassReflection $classReflection): Type
 			} elseif (
 				$lowercasedClassName === 'parent'
 				&& $classReflection !== null
-				&& $classReflection->getParentClass() !== false
+				&& $classReflection->getParentClass() !== null
 			) {
 				$typeClassName = $classReflection->getParentClass()->getName();
 			}
diff --git a/src/Type/Php/GetParentClassDynamicFunctionReturnTypeExtension.php b/src/Type/Php/GetParentClassDynamicFunctionReturnTypeExtension.php
index 41caad5470..8dbcd52c3a 100644
--- a/src/Type/Php/GetParentClassDynamicFunctionReturnTypeExtension.php
+++ b/src/Type/Php/GetParentClassDynamicFunctionReturnTypeExtension.php
@@ -92,7 +92,7 @@ private function findParentClassType(
 	): Type
 	{
 		$parentClass = $classReflection->getParentClass();
-		if ($parentClass === false) {
+		if ($parentClass === null) {
 			return new ConstantBooleanType(false);
 		}
 
diff --git a/src/Type/TypehintHelper.php b/src/Type/TypehintHelper.php
index 5fe0ed14fa..68b2a60e82 100644
--- a/src/Type/TypehintHelper.php
+++ b/src/Type/TypehintHelper.php
@@ -43,7 +43,7 @@ private static function getTypeObjectFromTypehint(string $typeString, ?string $s
 				$broker = Broker::getInstance();
 				if ($selfClass !== null && $broker->hasClass($selfClass)) {
 					$classReflection = $broker->getClass($selfClass);
-					if ($classReflection->getParentClass() !== false) {
+					if ($classReflection->getParentClass() !== null) {
 						return new ObjectType($classReflection->getParentClass()->getName());
 					}
 				}
diff --git a/tests/PHPStan/Reflection/ClassReflectionTest.php b/tests/PHPStan/Reflection/ClassReflectionTest.php
index 63d810a67a..fe893f3f61 100644
--- a/tests/PHPStan/Reflection/ClassReflectionTest.php
+++ b/tests/PHPStan/Reflection/ClassReflectionTest.php
@@ -141,7 +141,7 @@ public function testGenericInheritance(): void
 		$this->assertSame('GenericInheritance\\C', $reflection->getDisplayName());
 
 		$parent = $reflection->getParentClass();
-		$this->assertNotFalse($parent);
+		$this->assertNotNull($parent);
 
 		$this->assertSame('GenericInheritance\\C0<DateTime>', $parent->getDisplayName());