Resource type "Publication / Conference paper" should not fall back to BibTeX type "proceedings"

[ptamarit]

A user reported the case of a record of type "Publication / Conference paper".
They did not realize that they had to fill in the field "Book or report title" (aka imprint:imprint.title) in order for the record to serialize to the BibTeX type "in_proceedings" (thanks to this field mapping to the required BibTeX type "booktitle").
Instead, since this field was missing, the record serialized to the BibTeX type "proceedings" as a fallback.
As a consequence, the "author" field was missing from the BibTeX export, since "proceedings" does not have an "author" field.

The user thinks that we should remove the "proceedings" fallback and fall back to "misc" instead.
The reasoning is that a Conference paper will never be a complete proceedings.
Another benefit would be that "misc" would not lose the authors, and entering authors is the by far the most difficult part of a editing a BibTeX entry.