Added check_field_is_empty decorator to cleaning.py.
This makes sure the cleaning checks are skipped when a field is empty. Note that Djanog will raise it's own ValidationError when a required field is empty before attempting to clean it.
Patch by: Lennard de Rijk
Reviewed by: to-be-reviewed.
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html