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 getCommandFromCache() {
        assertSame(SmtpCommand.DATA, SmtpCommand.valueOf("DATA"));
        assertSame(SmtpCommand.EHLO, SmtpCommand.valueOf("EHLO"));
        assertNotSame(SmtpCommand.EHLO, SmtpCommand.valueOf("ehlo"));
    }