Netbeans插件：非法状态错误

Question

所以我继续按照this教程尝试我的第一个NB插件。

我收到以下错误：

java.lang.IllegalStateException: Lexer org.htm.lexer.HTMLexer@6787f302
  returned null token but lexerInput.readLength()=2
  lexer-state: null
  tokenStartOffset=8, readOffset=10, lookaheadOffset=11

我的语法是：

options {
  JAVA_UNICODE_ESCAPE = true;
  ERROR_REPORTING = false;
  STATIC = false;
  COMMON_TOKEN_ACTION = false;
  TOKEN_FACTORY = "Token";
  JDK_VERSION = "1.8";
  BUILD_PARSER = false;
}

PARSER_BEGIN(HTMLParser)

package org.html.jcclexer;

import java.io.*;

/**
 * Grammar to parse Java version 1.5
 * @author Sreenivasa Viswanadha - Simplified and enhanced for 1.5
 */

public class HTMLParser {}

PARSER_END(HTMLParser)

/* WHITE SPACE */

TOKEN :
{
  < WHITESPACE:
  " "
| "\t"
| "\n"
| "\r"
| "\f">
}

TOKEN   : { < HTML : "html" > }
MORE :
{
  < ~[] >
}

HTMLexer.java

public org.netbeans.api.lexer.Token<HTMTokenId> nextToken() 
    {
        try
        {

            Token token = javaParserTokenManager.getNextToken();
            System.out.println("Token Info Begins");
            System.out.println(token.image);
            System.out.println(token.next);
            System.out.println("Token Info Ends");
            if (info.input().readLength() < 1) 
            {
                return null;
            }
            return info.tokenFactory().createToken(HTMLanguageHierarchy.getToken(token.kind));
        }
        catch(Exception ex)
        {
            System.out.println(ex.getLocalizedMessage());
            return null;
        }
    }