protected function checkClassForCompability( $className ) {
    $result = $className;
    if( isset( DeferredExceptionsGlobal::$defExcClasses [$className])){
       if( ! DeferredExceptionsGlobal::$defExcClasses [$className] ){
         $result = null;
       }
    } else {
      if( ! class_exists( $className ) || ! is_subclass_of( $className, 'Exception')) {
        DeferredExceptionsGlobal::$defExcClasses [$className] = false;
        $result = null;
      } else {
        DeferredExceptionsGlobal::$defExcClasses [$className] = true;
      }
    }
    return $result;
  }