AttachmentClauseQueryFactory

Generates a lucene query for the passed TerminalClause. It is the responsibility of the factory to look at the Operator and Operand in the Termincal and generate a Lucene search for it. This method is only called after JIRA works out that the TermincalClause is relevant to this ClauseQueryFactory. A ClauseFactory needs to be careful when implementing the NOT_LIKE, NOT_EQUALS or NOT_IN operators. These negative operators should not match what is considered EMPTY. For example, the query "resolution is EMPTY" will return all unresolved issues in JIRA. The query "resolution != fixed" will only return all resolved issues that have not been resolved as "fixed", that is, it will not return any unresolved issues. The user would have to enter the query "resolution != fixed or resolution is EMPTY" to find all issues that are either unresolved or not resolved as "fixed". The ClauseQueryFactory must handle the situation when an invalid TerminalClause is passed. The ClauseQueryFactory must return an empty Lucene Search if the passed TerminalClause is invalid. Most importantly, ClauseQueryFactory may not throw an exception on the input of an invalid TermincalClause.