Previously `UILayout.prop_decorator()` (or `uiItemDecoratorR()` in C) only worked for single items, not for arrays. The decorators are added vertically, like `UILayout.prop()` adds them. This will be needed for adding decorators to material properties, but will likely have other use-cases as well. Also, `None` (or `NULL`) can be passed for the data-pointer and property now to create blank decorators (as already possible for `uiItemDecoratorR_prop` in C).