Missing check of presence of field

[treiher]

It shouldn't be allowed to reference fields in a condition which are potentially not present.

package Test is

   type M is
      message
         A : Boolean
            then B
               if A = True
            then C
               if A = False;
         B : Boolean;
         C : Boolean
            then null
               if B = False;
      end message;

end Test;