Null error while writing XMP metadata

[homocomputeris]

ArchLinux package by j0hannes #5299

JabRef 5.0.0-dev--2019-10-14----d2ddff574
Linux 5.3.6-zen1-1-zen amd64 
Java 12.0.2

$ java --version
openjdk 11.0.4 2019-07-16
OpenJDK Runtime Environment (build 11.0.4+11)
OpenJDK 64-Bit Server VM (build 11.0.4+11, mixed mode)
$ archlinux-java status
Available Java environments:
  java-11-openjdk (default)

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

An error with no description:

Author2000
Error while writing '/home/user/Documents/Literature/TPSA.pdf':
null

Finished writing XMP for 0 file (0 skipped, 1 errors).
Happens with different PDFs.
The event log is empty.

Steps to reproduce the behavior:

1. Create an entry
2. Add link to a local PDF in the General tab
3. Select this file
4. Tool - Write XMP...
5. A pop-up appears

[koppor]

@homocomputeris Are the PDFs freely available? It would be nice if you added them via a PR so that we can create test cases.

• PDF directory for tests: https://github.com/JabRef/jabref/tree/master/src/test/resources/pdfs
• bib files: https://github.com/JabRef/jabref/tree/master/src/test/resources/testbib (or add the bib files as skeleton java code or just as text in the PR)

[homocomputeris]

The one from my snippet is https://agenda.infn.it/event/2620/attachments/29206/34301/TPSA.pdf

Basically, it doesn't write to any PDF.
For example, from these links I downloaded jabref-authors.bib and one PDF, and, say, I want to write the 1st entry metadata to the PDF:

GarridoKallstromKummEtAl2016
  Error while writing '/home/user/Documents/Literature/thesis-example.pdf':
    null

Finished writing XMP for 0 file (0 skipped, 1 errors).

[homocomputeris]

I tried it today with the latest snapshot on Windows 10: the same null error is raised

[Siedlerchr]

Thanks to @tobiasdiez this issue should be fixed now

We would like to ask you to use a development build from https://builds.jabref.org/master and report back if it works for you. Please remember to make a backup of your library before trying-out this version.