QueryParser currently throws an exception if a wildcard term begins with the '?' operator.
The current documentation describes why this is:
In the flexible indexing branch, wildcard queries with leading '?' operator are no longer slow on big indexes (they do not enumerate terms in linear fashion).
Thus, it no longer makes sense to throw a ParseException for a leading '?'
So, users should be able to perform a query of "?foo" and no longer get a ParseException from the QueryParser.
For the flexible indexing branch, wildcard queries of 'foo?', '?foo', 'f?oo', etc are all the same from a performance perspective.