gexiv2: Error in gtkdoc helper script

[Schamschula (Marius Schamschula)]

While upgrading to gexiv2 I get the following error

ERROR: Error in gtkdoc helper script:

ERROR: ['/opt/local/bin/gtkdoc-fixxref', '--module=gexiv2', '--module-dir=html'] failed with status 1
Traceback (most recent call last):
  File "/opt/local/bin/gtkdoc-fixxref", line 57, in <module>
    fixxref.Run(options)
  File "/opt/local/share/gtk-doc/python/gtkdoc/fixxref.py", line 51, in Run
    LoadIndicies(options.module_dir, options.html_dir, options.extra_dir)
  File "/opt/local/share/gtk-doc/python/gtkdoc/fixxref.py", line 74, in LoadIndicies
    dir = common.GetModuleDocDir('glib-2.0')
  File "/opt/local/share/gtk-doc/python/gtkdoc/common.py", line 107, in GetModuleDocDir
    path = subprocess.check_output([config.pkg_config, '--variable=prefix', module_name], universal_newlines=True)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 411, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 489, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 854, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 1702, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
PermissionError: [Errno 13] Permission denied: ''