Fix issue with deserialization of payload that contain additional repeated fields

Author: Havret

src/Protobuf.System.Text.Json/ProtobufConverter.cs

@@ -72,10 +72,16 @@ public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerial
                 break;
             }
 
+            if (reader.TokenType != JsonTokenType.PropertyName)
+            {
+                reader.Read();
+                continue;
+            }
+
             var propertyName = reader.GetString();
             reader.Read();
-            
-            if (!_fieldsLookup.TryGetValue(propertyName, out var fieldInfo))
+
+            if (propertyName == null || !_fieldsLookup.TryGetValue(propertyName, out var fieldInfo))
             {
                 continue;
             }

test/Protobuf.System.Text.Json.Tests/ContractEvolutionTests.cs

@@ -16,6 +16,7 @@ public void Should_deserialize_a_new_version_of_a_message_using_the_old_version_
         {
             DoubleProperty = 1d,
             FloatProperty = 2f,
+            RepeatedInt32Property = {1, 2, 3}
         };
         var jsonSerializerOptions = TestHelper.CreateJsonSerializerOptions();
 
@@ -27,4 +28,23 @@ public void Should_deserialize_a_new_version_of_a_message_using_the_old_version_
         deserialized.ShouldNotBeNull();
         deserialized.DoubleProperty.ShouldBe(msg.DoubleProperty);
     }
+    
+    [Fact]
+    public void Should_deserialize_the_old_version_of_a_message_using_the_new_version_of_the_contract()
+    {
+        // Arrange
+        var msg = new MessageWithVersionMismatch
+        {
+            DoubleProperty = 1d,
+        };
+        var jsonSerializerOptions = TestHelper.CreateJsonSerializerOptions();
+
+        // Act
+        var payload = JsonSerializer.Serialize(msg, jsonSerializerOptions);
+        var deserialized = JsonSerializer.Deserialize<MessageWithVersionMismatchV2>(payload, jsonSerializerOptions);
+
+        // Assert
+        deserialized.ShouldNotBeNull();
+        deserialized.DoubleProperty.ShouldBe(msg.DoubleProperty);
+    }
 }

test/Protobuf.System.Text.Json.Tests/Protos/message_with_version_mismatch.proto

@@ -9,4 +9,5 @@ message MessageWithVersionMismatch {
 message MessageWithVersionMismatchV2 {
   double double_property = 1;
   float float_property = 2;
+  repeated int32 repeated_int_32_property = 3;
 }