Null value in Roles-file causes issue during update

[lafe]

When I tried to update from 5.2 to 6.3, I encountered the following issue during migration:

System.ArgumentNullException: Value cannot be null.
Parameter name: key
at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
at Bonobo.Git.Server.Data.Update.ADBackendUpdate.Pre600UpdateTo600.UpdateRoles(String dir, Dictionary`2 users)
at Bonobo.Git.Server.Data.Update.ADBackendUpdate.Pre600UpdateTo600.UpdateADBackend()
at Bonobo.Git.Server.MvcApplication.Application_Start()

Reason for this error was that the roles JSON file contained the null value in the members array. As I never edited the files in "App_Data" manually, I suspect that there was an issue in a previous version that caused this.