Volume not generating bibtex without <frontmatter>?

> `` is just the special stub for paper 0. If we don't generate it, then no bibtex is generated for the volume itself. We want to generate this volume bibtex even if there is no PDF. (If there _is_ a PDF, we add a `` tag within frontmatter, as we do for papers.) This is all a separate issue.

_Originally posted by @mjpost in https://github.com/acl-org/acl-anthology/issues/2724#issuecomment-1669528983_

This sounds like a bug, and the fix should be made in the code rather than generating `` blocks that reference non-existant frontmatter. I know the code is already intended to support proper processing of volumes without frontmatter, as there are comments to that effect.

Start by searching the Python code for bibtex generation and comments about processing volumes without frontmatter. Reproduce with a volume that has no block and confirm no volume bibtex is generated. Done means the volume bibtex is produced without creating fake frontmatter, while existing PDF/url handling still works.

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