public function isEmpty()
    {
        return $this->y === 0 && $this->m === 0 && $this->d === 0 && $this->h === 0 && $this->i === 0 && $this->s === 0;
    }
public function isEmpty()
    {
        return $this->y === 0 && $this->m === 0 && $this->d === 0 && $this->h === 0 && $this->i === 0 && $this->s === 0;
    }
public function isEmpty ( ) { return $ this -> y === 0 && $ this -> m === 0 && $ this -> d === 0 && $ this -> h === 0 && $ this -> i === 0 && $ this -> s === 0 ; }
Is this interval empty?
@return bool
Is this interval empty?