check if the mappable contains the data
if not, do not return a value
see https://github.com/psyplot/psy-view/issues/26
-
Tests passed (for all non-documentation changes) -
Fully documented, including CHANGELOG.rst
for all changes
if not, do not return a value
see https://github.com/psyplot/psy-view/issues/26
CHANGELOG.rst
for all changes