Using 2.0.0 RC1 the following message is shown:

Even when the source branch does exist remotely.

This is happening because BranchValidator is first called with null before being called with the BranchModel.

Looking into this more, what is happening is:

• Branches is set from Initialize
• Because Branches has changed the UI layer's selection is no longer valid so it sets its selection to null
• This selection is two-way bound to SourceBranch so this is set to null
• The BranchValidator notices this and things that the source branch doesn't exist remotely
• This line is then triggered, setting the SourceBranch
• BranchValidator is called again with the correct info and the validation passes, but at this point it's too late - the notification has already been sent.