PHP Manual: Maps to facet.missing

Description

public SolrQuery SolrQuery::setFacetMissing(bool $flag, string $field_override = ?)

Used to indicate that in addition to the Term-based constraints of a facet field, a count of all matching results which have no value for the field should be computed

Parameters

flag: true turns this feature on. false disables it.
field_override: The name of the field.

Return Values

Returns the current SolrQuery object, if the return value is used.