Error adding wikidata tag to OSM

[hroest]

I tried to add a wikidata tag to OSM and ran into the following error:

File "<string>", line 1lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1

URL: https://osm.wikidata.link/add_wikidata_tag

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/flask_sockets.py", line 40, in __call__
    handler, values = adapter.match()
  File "/usr/lib/python3/dist-packages/werkzeug/routing.py", line 1799, in match
    raise NotFound()
werkzeug.exceptions.NotFound: 404 Not Found: The requested URL was not found on the server. If you entered the URL manually please check your spelling and try again.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python3/dist-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/srv/osm-wikidata/matcher/view.py", line 275, in add_wikidata_tag
    root = etree.fromstring(r.content)
  File "src/lxml/etree.pyx", line 3235, in lxml.etree.fromstring
    
  File "src/lxml/parser.pxi", line 1876, in lxml.etree._parseMemoryDocument
    
  File "src/lxml/parser.pxi", line 1764, in lxml.etree._parseDoc
    
  File "src/lxml/parser.pxi", line 1127, in lxml.etree._BaseParser._parseDoc
    
  File "src/lxml/parser.pxi", line 601, in lxml.etree._ParserContext._handleParseResultDoc
    
  File "src/lxml/parser.pxi", line 711, in lxml.etree._handleParseResult
    
  File "src/lxml/parser.pxi", line 640, in lxml.etree._raiseParseError
    
File "<string>", line 1
lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1