Unclear behavior of ValidatePropertyAsync in ValidatingModelBase

[Garzuuhl]

Hey all,
a long time ago (#11) there were some changes to the ValidatePropertyAsync method. I don't know if I use this the right way, but if I call NotifyOfPropertyChanged with null or string.Empty it does not validate the full model, instead it calls Validator.ValidatePropertyAsync(string.Empty).
I reverted the change to ValidatePropertyAsync in 35c1b33 to see if this fixes my problem, it did, but I don't know if this breaks something else.

Before 35c1b33:

        protected virtual async Task<bool> ValidatePropertyAsync([CallerMemberName] string propertyName = null)
        {
            if (this.Validator == null)
                throw new InvalidOperationException("Can't run validation if a validator hasn't been set");

            if (String.IsNullOrEmpty(propertyName))
                return await this.ValidateAsync().ConfigureAwait(false);

            // To allow synchronous calling of this method, we need to resume on the ThreadPool.
            // Therefore, we might resume on any thread, hence the need for a lock
            var newErrorsRaw = await this.Validator.ValidatePropertyAsync(propertyName).ConfigureAwait(false);
.
.
.

After 35c1b33:

        protected virtual async Task<bool> ValidatePropertyAsync([CallerMemberName] string propertyName = null)
        {
            if (this.Validator == null)
                throw new InvalidOperationException("Can't run validation if a validator hasn't been set");

            if (propertyName == null)
                propertyName = String.Empty;

            // To allow synchronous calling of this method, we need to resume on the ThreadPool.
            // Therefore, we might resume on any thread, hence the need for a lock
            var newErrorsRaw = await this.Validator.ValidatePropertyAsync(propertyName).ConfigureAwait(false);
.
.
.

Thank you for this great framework!
Regards
Philipp