writeTerm
open override fun writeTerm(term: BytesRef, termsEnum: TermsEnum, docsSeen: FixedBitSet, norms: NormsProducer?): BlockTermState?
Write all postings for one term; use the provided TermsEnum to pull a [ ]. This method should not re-position the TermsEnum! It is already positioned on the term that should be written. This method must set the bit in the provided FixedBitSet for every docID written. If no docs were written, this method should return null, and the terms dict will skip the term.