public static SmtpCommand valueOf(CharSequence commandName) {
        ObjectUtil.checkNotNull(commandName, "commandName");
        SmtpCommand command = COMMANDS.get(commandName.toString());
        return command != null ? command : new SmtpCommand(AsciiString.of(commandName));
    }
@Test
    public void equalsIgnoreCase() {
        assertEquals(SmtpCommand.MAIL, SmtpCommand.valueOf("mail"));
        assertEquals(SmtpCommand.valueOf("test"), SmtpCommand.valueOf("TEST"));
    }