AssignmentToVoid

Emitted when assigning from a function that returns void:

<?php

function foo() : void {}
$a = foo();

Why this is bad

Though void-returning functions are treated by PHP as returning null (so this on its own does not lead to runtime errors), void is a concept more broadly in programming languages which is not designed for assignment purposes.

How to fix

You should just be able to remove the assignment entirely:

<?php

function foo() : void {}
foo();