SolrCollapseFunction::setNullPolicy Sets the NULL Policy &reftitle.description; public SolrCollapseFunctionSolrCollapseFunction::setNullPolicy stringnullPolicy Sets the NULL Policy. One of the 3 policies defined as class constants shall be passed. Accepts ignore, expand, or collapse policies. &reftitle.parameters; nullPolicy &reftitle.returnvalues; SolrCollapseFunction