In my project I implement a NullFieldFilter, which will filter the docs index some field regardless the value.
The implementation is traverse the index field use TermsEnum and PostingsEnum, or using DocValues advance function to traverse the docs which have this field. In this way I get FixedBitSet and cache it. btw: I am not sure if there is any simpler way to get this FixedBitSet. In lucene 7 there is no filter any longer, so I need convert this FixedBitSet to a ConstantScoreQuery and then construct a FILTER Clause with this ConstantScoreQuery. So how to construct a ConstantScoreQuery with FixedBitSet?
