Deal with arXiv entries of published journals whose DOI is not on the arXiv entry

[mseri]

Some authors do not upload their DOI to arXiv but only the journal reference.

In this case it would be nice to be able to generate the correct journal bibtex. It could be done from the journal reference (which would be messy and complicated), or one could use the presence of the journal reference to try and find the DOI, then use the DOI to get the bibtex entry.