Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references

CHANGELOG

@@ -5,6 +5,7 @@ v 8.13.0 (unreleased)
   - Speed-up group milestones show page
   - Log LDAP lookup errors and don't swallow unrelated exceptions. !6103 (Markus Koller)
   - Add more tests for calendar contribution (ClemMakesApps)
+  - Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references
   - Fix robots.txt disallowing access to groups starting with "s" (Matt Harrison)
   - Only update issuable labels if they have been changed
   - Revoke button in Applications Settings underlines on hover.

lib/banzai/reference_parser/base_parser.rb

@@ -79,8 +79,12 @@ module Banzai
       def referenced_by(nodes)
         ids = unique_attribute_values(nodes, self.class.data_attribute)
 
+        if ids.empty?
+          references_relation.none
+        else
           references_relation.where(id: ids)
         end
+      end
 
       # Returns the ActiveRecord::Relation to use for querying references in the
       # DB.