<!-- Please make the PR against the `master` branch. -->

 - [ ] Closes #xxxx <!-- remove if there is no corresponding issue, which should only be the case for minor changes -->
 - [ ] Tests added <!-- for all bug fixes or enhancements -->
 - [ ] Tests passed <!-- for all non-documentation changes -->
 - [ ] Passes ``git diff origin/master **/*py | flake8 --diff`` <!-- remove if you did not edit any Python files  -->
 - [ ] Fully documented <!-- remove if this change should not be visible to users, e.g., if it is an internal clean-up, or if this is part of a larger project that will be documented later -->
