diff --git a/src/Enum.php b/src/Enum.php
index b47875d..8686873 100644
--- a/src/Enum.php
+++ b/src/Enum.php
@@ -18,6 +18,11 @@ abstract class Enum implements JsonSerializable
     /** @var string */
     protected $value;
 
+    /**
+     * @param string $value
+     *
+     * @return static
+     */
     public static function from(string $value): Enum
     {
         if (method_exists(static::class, $value)) {
@@ -37,6 +42,10 @@ public function __construct(string $value = null)
             throw new TypeError("Value {$value} not available in enum ".static::class);
         }
 
+        if ($value === null) {
+            throw new TypeError("Value of enum can't be null");
+        }
+
         $this->value = $value;
     }
 
@@ -73,9 +82,13 @@ public function equals($enum): bool
         return true;
     }
 
+    /**
+     * @param \Spatie\Enum\Enum[] $enums
+     *
+     * @return bool
+     */
     public function isOneOf(array $enums): bool
     {
-        /** @var \Spatie\Enum\Enum $enum */
         foreach ($enums as $enum) {
             if ($this->equals($enum)) {
                 return true;
@@ -112,14 +125,14 @@ public static function getValues(): array
 
     protected static function resolve(): array
     {
+        $enumValues = [];
+
         $class = static::class;
 
         if (isset(self::$cache[$class])) {
             return self::$cache[$class];
         }
 
-        $enumValues = [];
-
         $staticReflection = new ReflectionClass(static::class);
 
         foreach (self::resolveValuesFromStaticMethods($staticReflection) as $value => $name) {
@@ -130,15 +143,11 @@ protected static function resolve(): array
             $enumValues[$value] = $name;
         }
 
-        self::$cache[$class] = $enumValues;
-
-        return self::$cache[$class];
+        return self::$cache[$class] = $enumValues;
     }
 
     protected static function resolveValuesFromStaticMethods(ReflectionClass $staticReflection): array
     {
-        $enumValues = [];
-
         $selfReflection = new ReflectionClass(self::class);
 
         $selfStaticMethods = [];
@@ -147,6 +156,7 @@ protected static function resolveValuesFromStaticMethods(ReflectionClass $static
             $selfStaticMethods[$method->name] = $method->name;
         }
 
+        $enumValues = [];
         foreach ($staticReflection->getMethods(ReflectionMethod::IS_STATIC) as $method) {
             $methodName = $method->getName();