Observed behaviour:
Some PDF files are imported as invalid Bibtex records of type @Misc with empty Bibtexkey and with only one field file. I suppose, this is caused the failure to extract DOI from the first page of a PDF file. (JabRef docs say "In case a DOI is found on the first page, the DOI is used to generate the BibTeX information")

Expected behaviour:
JabRef extracts DOI from the PDF and retrieves the necessary information from the internet.

Steps to reproduce the observed behavior:

1. Download the pdf file
2. In JabRef: Lookup -> Search for unlinked local files; scan the directory with the file, select the file, proceed to Import.
3. Observe a new record in the database, which looks as follows:
   

JabRef version
JabRef 5.1--2020-06-02--46fd96b
Windows 10 10.0 amd64
Java 14.0.1

• Mandatory: I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists