Add a new conformance test for top level JSON null (#5966)

* Add a new conformance test for top level JSON null

conformance/binary_json_conformance_suite.cc

@@ -2452,6 +2452,8 @@ void BinaryAndJsonConformanceSuite::RunSuiteImpl() {
         "unknown": {"a": 1}
       })",
       "");
+
+  ExpectParseFailureForJson("RejectTopLevelNull", REQUIRED, "null");
 }
 
 }  // namespace protobuf

conformance/failure_list_php_c.txt

@@ -43,3 +43,4 @@ Required.Proto3.ProtobufInput.DoubleFieldNormalizeSignalingNan.JsonOutput
 Required.Proto3.ProtobufInput.FloatFieldNormalizeQuietNan.JsonOutput
 Required.Proto3.ProtobufInput.FloatFieldNormalizeSignalingNan.JsonOutput
 Required.Proto3.ProtobufInput.ValidDataRepeated.FLOAT.JsonOutput
+Required.Proto3.JsonInput.RejectTopLevelNull

conformance/failure_list_ruby.txt

@@ -65,3 +65,4 @@ Required.Proto3.JsonInput.IgnoreUnknownJsonNumber.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonObject.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonString.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonTrue.ProtobufOutput
+Required.Proto3.JsonInput.RejectTopLevelNull

conformance/failure_list_ruby_mac.txt

@@ -70,3 +70,4 @@ Required.Proto3.JsonInput.IgnoreUnknownJsonObject.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonString.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonTrue.ProtobufOutput
 Recommended.Proto3.JsonInput.FieldMaskInvalidCharacter
+Required.Proto3.JsonInput.RejectTopLevelNull