Description:
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According to php.net

abs ( mixed $number ) : int|float


mixed is equivalent to the union type array|bool|callable|int|float |object|resource|string|null . Available as of PHP 8.0.0.

So abs should take a string.  Instead we get a fatal error

Fatal error: Uncaught TypeError: abs(): Argument #1 ($num) must be of type int|float, string

Test script:
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abs('');

Expected result:
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0

Actual result:
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Fatal error: Uncaught TypeError: abs(): Argument #1 ($num) must be of type int|float, string