Empty declension tables

Hi. For some unknown reason to me the declension tables of certain Swedish nouns don't show any declension form but remain empty. For instance, this term: biltvätt. While some templates are ok. any of the declension tables of nouns that use the Template:sv-noun-reg-ar remain empty. My question is now: Why is this so and is this intended?

Next question is about uncountable nouns. In the Swedish wiktionary the noun tvätt is uncountable while the entry here also offers a plural. Which one is the correct form.

I faced both questions when I was creating the entry hjärntvätt. That's why I'm asking. Thanks.