diff --git a/src/Forms/Controls/ChoiceControl.php b/src/Forms/Controls/ChoiceControl.php
index 9095c4af8..3d36d4de1 100644
--- a/src/Forms/Controls/ChoiceControl.php
+++ b/src/Forms/Controls/ChoiceControl.php
@@ -85,7 +85,7 @@ public function getValue(): mixed
 	/**
 	 * Returns selected key (not checked).
 	 */
-	public function getRawValue(): string|int
+	public function getRawValue(): string|int|null
 	{
 		return $this->value;
 	}
diff --git a/src/Forms/Helpers.php b/src/Forms/Helpers.php
index 6d1a13179..3a2fdb480 100644
--- a/src/Forms/Helpers.php
+++ b/src/Forms/Helpers.php
@@ -70,7 +70,7 @@ private static function sanitize(int $type, $value)
 	{
 		if ($type === Form::DataText) {
 			return is_scalar($value)
-				? Strings::normalizeNewLines($value)
+				? Strings::normalizeNewLines((string) $value)
 				: null;
 
 		} elseif ($type === Form::DataLine) {
diff --git a/src/Forms/Rendering/DefaultFormRenderer.php b/src/Forms/Rendering/DefaultFormRenderer.php
index 1f8336ec2..34ebcb936 100644
--- a/src/Forms/Rendering/DefaultFormRenderer.php
+++ b/src/Forms/Rendering/DefaultFormRenderer.php
@@ -117,7 +117,7 @@ class DefaultFormRenderer implements Nette\Forms\FormRenderer
 	];
 
 	protected Nette\Forms\Form $form;
-	protected int $counter;
+	protected int $counter = 0;
 
 
 	/**
diff --git a/src/Forms/Validator.php b/src/Forms/Validator.php
index bf3656bff..3a9645f21 100644
--- a/src/Forms/Validator.php
+++ b/src/Forms/Validator.php
@@ -376,7 +376,7 @@ public static function validateMimeType(Controls\UploadControl $control, $mimeTy
 	{
 		$mimeTypes = is_array($mimeType) ? $mimeType : explode(',', $mimeType);
 		foreach (static::toArray($control->getValue()) as $file) {
-			$type = strtolower($file->getContentType());
+			$type = strtolower($file->getContentType() ?? '');
 			if (!in_array($type, $mimeTypes, true) && !in_array(preg_replace('#/.*#', '/*', $type), $mimeTypes, true)) {
 				return false;
 			}