[plazma]

Hi, I'm working on Metadata (Source) plugin, and the source I'm using does not list ISBNs for every book.

Now, what happens is, that when I don't have the ISBN, I don't call the `self.plugin.cache_isbn_to_identifier` method. And if I don't do that, then the result is not listed, even if I add it to the result_queue.

When I create some dummy ISBN and call the cache method, then I see the result. But then the ISBN can be overwritten (if it already exists). Or, if I create an isbn that is bad (e.g. contains characters), then after the data is accepted, it shows that the ISBN is wrong (because that identifier uses special checks).

So, my question is, if the source for the book's metadata does not have the ISBN listed, what is the correct way to handle this, if I want it to be listed in the results? I couldn't find any documentation around this.