Include directives may be nil if no includes are directed

closes gh-1235

Author: hatch-carl

lib/jsonapi/request_parser.rb

@@ -265,7 +265,7 @@ def parse_filters(filters)
             return @errors.concat(Exceptions::FilterNotAllowed.new(filter_method).errors)
           end
 
-          unless @include_directives.include_config(relationship.name.to_sym).present?
+          unless @include_directives&.include_config(relationship.name.to_sym).present?
             return @errors.concat(Exceptions::FilterNotAllowed.new(filter_method).errors)
           end
 

test/controllers/controller_test.rb

@@ -2635,6 +2635,13 @@ def test_show_with_filters_and_included_resources_with_filters
     assert_equal 2, json_response['included'].size
     assert_equal '4', json_response['included'][0]['id']
   end
+
+  def test_show_with_filters_and_no_included_resources
+    get :show, params: { id: 1, filter: { 'paintings.category' => 'oil' } }
+    assert_response :bad_request
+    assert_equal('Filter not allowed', json_response['errors'][0]['title'])
+    assert_equal('category is not allowed.', json_response['errors'][0]['detail'])
+  end
 end
 
 class Api::V5::AuthorsControllerTest < ActionController::TestCase