Bug report

This is another attempt at issue #2727, I keep running into this problem as I often
use the shortcut if ($var == "") return; to catch both the empty string and false.

I understand it is fairly complicated to fully handle PHP's type coercion rules, but wouldn't it be possible and easy to code a special rule for this specific case? After all the if ($var) return; does work, the problem is that it also catches the string "0" which I usually find a bit disturbing.

Code snippet that reproduces the problem

<?php

/** @param string|false $a */
function f1($a): void {
  \PhpStan\DumpType($a);
  if (!$a) return;
  \PhpStan\DumpType($a);
}

/** @param string|false $a */
function f2($a): void {
  \PhpStan\DumpType($a);
  if ($a == "") return;
  \PhpStan\DumpType($a);
}

https://phpstan.org/r/a03da769-4d8e-41e0-a1eb-2d153c49792c

Expected output

  5      Dumped type: string|false
  7      Dumped type: non-empty-string
  12     Dumped type: string|false
  14     Dumped type: non-empty-string

Actual output

  5      Dumped type: string|false
  7      Dumped type: non-empty-string
  12     Dumped type: string|false
  14     Dumped type: string|false