-(Bool) isEmpty:(NSString *) str {

    if (!str) {
        return true;
    } else {
//A character set containing only the whitespace characters space (U+0020) and tab (U+0009) and the newline and nextline characters (U+000A–U+000D, U+0085).
        NSCharacterSet *set = [NSCharacterSet whitespaceAndNewlineCharacterSet];
 
//Returns a new string made by removing from both ends of the receiver characters contained in a given character set.
        NSString *trimedString = [str stringByTrimmingCharactersInSet:set];
 
        if ([trimedString length] == 0) {
            return true;
        } else {
            return false;
        }
    }
}