scripting: fix javadoc error: unknown tag: null

Change-Id: I7d9ec1759a1689943d51636926024278cec0dc3b
Reviewed-on: https://gerrit.libreoffice.org/11234
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>