TestNullWithBoolReturnType.php

<?php
function foo(): bool {
    return null;
}
try {
    var_dump(foo());
}
catch (Throwable $t) {
    // Executed only in PHP 7, catches errors and exceptions
    echo "Throwable: {$t->getMessage()}\n";
}
catch (Exception $e) {
    // Executed PHP7 and 5.x, catches exceptions
    // ::NOTE:: Redundant if your catching throwable in PHP7
    echo "Exception: {$e->getMessage()}\n";
}
catch (Error $e){
   //Executed only in PHP 7, catches errors
   //Type mismatch is a subclass of Error (TypeError) 
   //http://php.net/manual/en/class.typeerror.php
   // ::NOTE:: Redundant if your catching throwable in PHP7
}

//OUTPUT: Throwable: Return value of foo() must be of the type boolean, null returned
//NOTE: If we were to cast null as a boolean i.e. :
//return (bool) null;
//we would get false