Internal: non-strict checking leads to inconsistent behavior

[kkmuffme]

https://psalm.dev/r/30076adf91

There are phpcs rules that disallow this already, however it might be too intrusive, bc it will disallow this in all cases, instead of only when necessary (e.g. Squiz.Operators.ComparisonOperatorUsage.ImplicitFalse and Squiz.Operators.ComparisonOperatorUsage.ImplicitTrue or Squiz.Operators.ComparisonOperatorUsage)

There should be a psalm check for these, where a union of falsy types is flagged.

This is an internal issue (e.g. #10500 was only necessary bc of the non-strict checking) but I probably also affects psalm users's codebases.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/30076adf91

<?php

/**
 * @param array|null $arg
 * @return void
 */
function foo($arg) {
	if ($arg) {
    	// this is risky, bc the empty array and null case are handled together
    }
    
    if (!$arg) {
     	// this is risky, bc the empty array and null case are handled together  
    }
}

Psalm output (using commit a75d26a):

No issues!

[kkmuffme]

Will create a PR for this