"Source branch does not exist remotely" being shown when creating PR, though it does exist remotely

[grokys]

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.

[grokys]

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• Because Branches has changed the UI layer's selection is no longer valid so it sets its selection to null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.