False MixedArgument error when using php isset

[AlexMinaev19]

Psalm reports a false MiaxedArgument when using PHP isset.

https://psalm.dev/r/865dff4af9

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/865dff4af9

<?php

function f (int $a): int
{
    return $a;
}

if (rand(0, 100) === 23) {
    $a = 15;
}

if (isset($a)) {
    f($a);
}

Psalm output (using commit 16b24bd):

INFO: MixedArgument - 13:7 - Argument 1 of f cannot be mixed, expecting int