Method '__toString' return type

Reports the __toString methods that do not return string.

Prior to PHP 7.4, this would lead to a fatal E_RECOVERABLE_ERROR level error. In PHP 7.4, a fatal non-recoverable ERROR is thrown. In PHP 8.0, the return value follows the standard PHP type semantics and will be coerced into a string if possible and if strict typing is disabled.

See __toString (php.net) for details.