Major Description
As denoted in the ticket SOLR-7086 the DocumentDictionary entry iterator shouldn't skip entries from the dictionary having null value for the payload field due to the fact that this field is optional.
This behaviour causes inconsistencies in the Solr suggester which simply skips valid documents due to the fact that they don't have values for the payload field.
As agreed with mikemccand I am attaching a patch to this Lucene issue.