label: allow setting NULL for the text property
label: allow setting NULL for the text property

Removing the warning allows the "text" property to be bound to string
properties that do accept NULL, without causing a warning.

clutter-project/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,pwithnall/mx,pwithnall/mx