public IThemeEditorViewModel OpenMasterThemeForScript(IItemFilterScriptViewModel scriptViewModel)
        {
            var existingMasterThemeViewModelCount =
                OpenDocuments.OfType <IThemeEditorViewModel>()
                .Count(c => c.IsMasterThemeForScript == scriptViewModel.Script);

            if (existingMasterThemeViewModelCount > 0)
            {
                return(OpenDocuments.OfType <IThemeEditorViewModel>()
                       .First(c => c.IsMasterThemeForScript == scriptViewModel.Script));
            }

            return(null);
        }