To me there is no way to put by a dynamic manner every categories in that blank.
So you have two solutions :
Take every categories ID and put them in the blank.
Exemple : 1;2;3;4;5;6;7;8;9;10;11;17;18;19;20;21;22;23;24;25;26
''Hint: Categories ID are in the URL when you are in Admin categories.
Here 27 is the category ID.''
Put only one category in the blank and every time you create a new object (page), put it in this category.
In every cases:
You should establish the obligation of categories when editing a page.
Hope you a good day