Entity Framework Validation errors not being handled correctly by breeze.sharp client

Question

This issue is in the 0.5.4 release of Breeze.Sharp. Not sure if it should be fixed in Breeze.Sharp or perhaps Breeze.ContextProvider.EF6, but there seems to be a disconnect between expected behaviors.

Unexpected Behavior:

I have a .Net Web API BreezeController that contains an EF6 repository.

If I perform object level validation via BeforeSaveEntities override, where the guidance is to fail validation by throwing an EntityErrorsException, the Breeze.Sharp client catches this as expected and all is well.

If, however, I perform attribute level validation using an Entity Framework ValidationAttribute class, instead of an EntityErrorsException, failures are returned to the Breeze.Sharp client as a SaveResult containing an Errors collection. In this case, the client throws an exception: Unable to cast object of type 'Newtonsoft.Json.Linq.JValue' to type 'Newtonsoft.Json.Linq.JArray'. This exception occurs when Breeze.Sharp tries to parse the SaveResult's KeyMappings array, which is null.

Workaround:

For now, rather than changing all of my Validation Attributes to throw an EntityErrorsException, I resolved this in my BreezeController's SaveChanges method by checking the returning SaveResults for any errors, and if found, wrapping those errors in an exception that I then throw to the client:

[HttpPost]
public SaveResult SaveChanges(JObject saveBundle)
{
    var saveResult = _unitOfWork.Commit(saveBundle);
    if (saveResult.Errors != null && saveResult.Errors.Count > 0)
    {
        var errors = new List<EntityError>();
        foreach (var error in saveResult.Errors)
        {
            var entityError = error as EntityError; //errors are stored as List<object> in the SaveResult
            if (string.IsNullOrEmpty(entityError.ErrorMessage))
            {
                entityError.ErrorName = "Attribute Validation Error";
            }
            errors.Add(entityError);
        }
        throw new EntityErrorsException(errors);
    }
    return saveResult;
}