The current behavior when submitting an empty mail field in the RGW user form
that was previously filled was to replace it with "false".
This was a regression introduced through the use of "CdFormGroup" which had
a "_filterValue" method which converted empty strings into false, but it was
removed now.
Fixes: http://tracker.ceph.com/issues/26861 Signed-off-by: Stephan Müller <smueller@suse.com>