Error when using sphinx themes

[hplgit]

Making a sphinx document and using any of the themes (flat, dark, responsive, ...) that comes with tinkerer, results in a KeyError:

Exception occurred:
File "/usr/local/lib/python2.7/dist-packages/Tinkerer-1.5-py2.7.egg/tinkerer/ext/metadata.py", line 127, in process_metadata
while relations[doc][2]:
KeyError: 'master'

Full traceback in .log file:

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/sphinx/cmdline.py", line 244, in main
app.build(opts.force_all, filenames)
File "/usr/local/lib/python2.7/dist-packages/sphinx/application.py", line 287, in build
self.builder.build_update()
File "/usr/local/lib/python2.7/dist-packages/sphinx/builders/init.py", line 251, in build_update
'out of date' % len(to_build))
File "/usr/local/lib/python2.7/dist-packages/sphinx/builders/init.py", line 265, in build
self.doctreedir, self.app))
File "/usr/local/lib/python2.7/dist-packages/sphinx/environment.py", line 556, in update
for retval in app.emit('env-updated', self):
File "/usr/local/lib/python2.7/dist-packages/sphinx/application.py", line 536, in emit
results.append(callback(self, *args))
File "/usr/local/lib/python2.7/dist-packages/Tinkerer-1.5-py2.7.egg/tinkerer/ext/blog.py", line 70, in env_updated
metadata.process_metadata(app, env)
File "/usr/local/lib/python2.7/dist-packages/Tinkerer-1.5-py2.7.egg/tinkerer/ext/metadata.py", line 127, in process_metadata
while relations[doc][2]:
KeyError: 'master'

The sphinx file is minimalistic:

A title

Hello, World!