No feedback provided to the user when a mandatory date field is not filled in.

If a date field is mandatory but the user doesn't provide a date, the form will be reloaded upon submit but no error message will be given to the user. The call to form_set_error() has omitted the $component_key parameter, and so the form error is not properly set.

After applying this patch, the user will see an appropriate error message when attempting to submit a form with a mandatory date field that is not filled in.