Error Identifier: nullableType.mixed

Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

function doFoo(?mixed $value): void
{
}

Why is it reported? #

The type mixed cannot be used in a nullable type declaration (?mixed). The mixed type already includes null (it represents any type including null), so making it nullable is redundant and not allowed in PHP.

How to fix it #

Use mixed without the nullable modifier:

 <?php declare(strict_types = 1);
 
-function doFoo(?mixed $value): void
+function doFoo(mixed $value): void
 {
 }

Non-ignorable error #

This error cannot be ignored using @phpstan-ignore or the ignoreErrors configuration. Non-ignorable errors indicate code that would cause a crash or a fatal error at runtime, or a fundamental problem in the analysed code that must be addressed.

Rules that report this error #

PHPStan\Rules\Types\InvalidTypesInUnionRule [1]

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