@staticmethod
def p_directive_next(symbols):
    """directive_next : SPACE COLON directive_argument
                          | COLON directive_argument
                          | empty
        """
    if len(symbols) == 3:
        symbols[0] = symbols[2].strip()
    elif len(symbols) == 4:
        symbols[0] = symbols[3].strip()
    elif len(symbols) == 2 and symbols[1] == ':':
        symbols[0] = ''
    else:
        symbols[0] = None
