Crashed when starting SourceTree - although subsequently it didn't crash.

Stack trace:

2015-08-03T08:39:33: Fatal error:
System.NullReferenceException: Object reference not set to an instance of an object.

2015-08-03T08:39:33: Stack trace:
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at SourceTree.AppRoot.GetRepositoryForPath(String path, String name) in C:\projects\bitbucket.org\atlassian\sourcetreewin\AppRoot.cs:line 1804
at SourceTree.AppRoot.InitialiseRepositories(IEnumerable`1 list) in C:\projects\bitbucket.org\atlassian\sourcetreewin\AppRoot.cs:line 638
at SourceTree.AppRoot.LoadBookmarks() in C:\projects\bitbucket.org\atlassian\sourcetreewin\AppRoot.cs:line 528
at SourceTree.AppRoot.DoWindowStartupTasks() in C:\projects\bitbucket.org\atlassian\sourcetreewin\AppRoot.cs:line 1312
at SourceTree.ViewModel.MainWindowViewModel..ctor() in C:\projects\bitbucket.org\atlassian\sourcetreewin\ViewModel\MainWindowViewModel.cs:line 446
at SourceTree.MainWindow..ctor() in C:\projects\bitbucket.org\atlassian\sourcetreewin\MainWindow.xaml.cs:line 33
at SourceTree.AppRoot.OnStartup(StartupEventArgs e) in C:\projects\bitbucket.org\atlassian\sourcetreewin\AppRoot.cs:line 684
at SourceTree.App.OnStartup(StartupEventArgs e) in C:\projects\bitbucket.org\atlassian\sourcetreewin\App.xaml.cs:line 119
at System.Windows.Application.<ctor>b_0(Object unused)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)