changing a page title to space character (' ') makes a page immutable

if you edit a page in a space and change the title of the page to just a space character (' ') and save it the request will be ok and the page gets saved. the page title is then possibly shown as 'null'.

but now there is no possibility to change the page again because the title in the database for the corresponding page is '(null)' and every request (editing,removing,viewing the page in the page hierarchy of the space) results in errors. if you watch the alphabetical page listing of that space you will see a page with velocities unresolved page title ($webwork.htmlEncode($page.title)).

maybe there are more leaks i did not see.

i think a request to change a title to only a space character should generally be refused.