This inspection detects attempts to convert objects without __toString() method implementation to string,
since PHP 5.2.0, it would cause E_RECOVERABLE_ERROR.
"Check __toString exists for each expression type": if the option is on, the inspection will check all possible types of the expression and
report if at least one ot them doesn't contain __toString() method implementation.
http://www.php.net/manual/en/language.oop5.magic.php#object.tostring