Handle null value in CheckboxGroupInput

Release 0.7.2

Release 0.7.1

Merge pull request marmelab#224 from marmelab/next

Version 0.7.0

Release 0.6.2

Fix wrong dependency

Closes marmelab#187

Release v0.6.0

Publish bugfix release

Publish minor version

Release bugfix as v0.5.2