Strange error with NSSecureTextField in NSOpenPanel's accessory view

Question

in my app I use an NSOpenPanel with an accessory view. This view has, among other things, a NSSecureTextField. Every time I open the panel this notice shows up in the log:

NSSecureTextFieldCell detected a field editor ((null)) that is 
not a NSTextView subclass designed to work with the cell. Ignoring...

Does anybody know what exactly this means and how to get rid of it? For now it isn't causing any problems but I would like to remove this.

Thanks a lot!