[Gtk-sharp-list] ComboBox & gtk_entry_set_text: assertion `text != NULL' failed

[Adam Tauno Williams]

I've created a window in Glade, and use it in a C# app.  There are
several combo boxes,  one works fine and the others report a
"gtk_entry_set_text: assertion `text != NULL' failed" whenever you try
to select an item (the selection list displays just fine, but nothing is
selected).  The code to initialize the combo boxes (first one works,
second one doesn't) is: