If the date is not specified for a release, "null" is displayed in the header of that release. For example, the header text for release 1.0.0 is "Release 1.0.0 - null".
Note that the date is correctly left empty in the release table.
My suggestion is that if no date is specified, the header text should just be "Release x.x.x". No dash and obviously no "null" text.