Merge pull request rails#53325 from jeromedalbert/fix-controller-tests-content-type-error

Fix `NoMethodError` when content type is set to nil in tests

Author: kamipo

actionpack/lib/action_controller/test_case.rb

@@ -108,7 +108,7 @@ def assign_parameters(routes, controller_path, action, parameters, generated_pat
             set_header k, "application/x-www-form-urlencoded"
           end
 
-          case content_mime_type.to_sym
+          case content_mime_type&.to_sym
           when nil
             raise "Unknown Content-Type: #{content_type}"
           when :json

actionpack/test/controller/test_case_test.rb

@@ -627,6 +627,13 @@ def test_params_passing_doesnt_modify_in_place
     end
   end
 
+  test "nil Content-Type header with post request" do
+    @request.headers["Content-Type"] = nil
+    assert_raises(match: /Unknown Content-Type/) do
+      post :render_body
+    end
+  end
+
   def test_using_as_json_sets_request_content_type_to_json
     post :render_body, params: { bool_value: true, str_value: "string", num_value: 2 }, as: :json