I was using org.apache.lucene.queryParser.QueryParser for parsing the input.
Input query string: "category: (4 or 6 or 8)"
QueryParser's parse() method is resulting in Null Pointer Exception.
If i give input query string as "category: (4 OR 6 OR 8)" which is uppercase 'OR', it works fine and i get the desired results.
I'm seeing the problem only with lower case 'or'