It looks like the issue does not exists.

I have thinked that i compare

 

NOT 

     (

     EXISTS()

     OR

     EXISTS()

     )

 

but this was really NOT EXISTS AND SOMETHING or EXISTS

 

and logic table for "NOT EXISTS AND SOMETHING" is:

 

false and NULL = false 

but 

true and NULL = NULL 

 

which is now understandable

 

thank you for your time

Karol Bieniaszewski