-(Boolean) isEmptyOrNull:(NSString *) str {   if (!str) {     // null object     return true;   }else if(str == Null){ return true; }else if([str isKindOfClass:[NSNull class]]){     return true;   }else {     NSString *trimedString = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];     if ([trimedString length] == 0) {       // empty string       return true;     } else {       // is neither empty nor null       return false;     }   } }