Did overwrite already set props with "".

This overwrites the handleUpdateAfterCreateOrPatch method of the
createOrPatchMixin and adapts it to work with documentations that
where send by the backend as either already created or dummy.

data = data.data[mutation.definitions[0].name.value].items;
breaks if not both names in definition are the same

Initial version for desktop & edit.
Will update for mobile.

Now it works with the createOrPatchMixin.
Suggestion is to really standardize on batch mutations.

instead of stringyfied key

The queryMixin assumes query results are named items.
It's already customary in other queries.
Dynamically detecting and adapting the item name is not possible.