Running `Biber' on `handout' with ``biber handout''
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LC_ALL = (unset),
    LANG = "en_DE.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
INFO - This is Biber 2.12
INFO - Logfile is 'handout.blg'
INFO - Reading 'handout.bcf'
INFO - Found 0 citekeys in bib section 0
WARN - The file 'handout.bcf' does not contain any citations!
INFO - Writing 'handout.bbl' with encoding 'UTF-8'
INFO - Output to handout.bbl
INFO - WARNINGS: 1