Don't return nil for missing objects from parser cache

changelogs/unreleased/dm-fix-parser-cache.yml

@@ -0,0 +1,4 @@
+---
+title: Don't return nil for missing objects from parser cache
+merge_request:
+author:

lib/banzai/reference_parser/base_parser.rb

@@ -171,7 +171,7 @@ module Banzai
             collection.where(id: to_query).each { |row| cache[row.id] = row }
           end
 
-          cache.values_at(*ids)
+          cache.values_at(*ids).compact
         else
           collection.where(id: ids)
         end

spec/lib/banzai/reference_parser/base_parser_spec.rb

@@ -114,7 +114,7 @@ describe Banzai::ReferenceParser::BaseParser, lib: true do
       expect(hash).to eq({ link => user })
     end
 
-    it 'returns an empty Hash when entry does not exist in the database' do
+    it 'returns an empty Hash when entry does not exist in the database', :request_store do
       link = double(:link)
 
       expect(link).to receive(:has_attribute?).