ExpandComponent has an equivalent to the collapse qparser bug tracked in
...has some very, very, old code/semantics in it that date back to when the FieldCache was incapable of differentiating between a document that contained '0' in the field being un-inverted, and a document that didn't have any value in that field.
This limitation does not exist in DocValues (nor has it existed for a long time) but as the DocValues API has evolved, and as the [...] code has been updated to take advantage of the newer APIs that make it obvious when a document has no value in a field, the [...] code still explicitly equates "0" in a numeric field with the "null group"
- relates to
SOLR-15047 'collapse' on numeric field treats all docs with '0' in collapse field as part of the null group
SOLR-14330 Return docs with null value in expand for field when collapse has nullPolicy=collapse