Null.Pointer Exception

snap
#1

I am currently trying to create a classification of polarimetric data. Whenever I want to run the supervised classification I receive the error message that the calculation can´t be run due to “null pointer exception”. Does anyone know what it means and how to solve it?

Thanks in advance!

#2

what data are you using?
what were the steps to pre-process the data?
which classification did you select?
what kind of training areas are you using?

#3

Meawhile I found a way of how to bypass the problem. I used Band Math to create a mask of the area.
Thank you for helping!