not existing = default
empty string = default
0 = default
1 = other meaning #1
2 = other meaning #2

So, there are three possible ways to achieve the default.

I want to show a popup for the choices. But I do not want to have
multiple choices for the various possible default values (empty and
zero) appear in the popup.

How do I achieve this? When I enter an empty string into the "Default
value" field, and even if I then also defined the empty string in the
plist, the popup still does not show that choice but shows an empty
choice instead.

Here's an example:

"Default" = "";
"meaning # 1" = "1";
"meaning #2" = "2";

Now, if the actual value in the prefs is non-existing or empty, I want
the unopened popup to show "Default". However, it shows an empty text
if the pref is non-existing, and only shows "Default" is the pref
exists with an empty value. And same problem if the value is 0.

You can see here what I've entered so far:

http://secrets.textdriven.com/preferences/edit/597