SQLite driver : Getting probelm with getBinaryStream whene Blob is null

I'm getting a problem with getBinaryStream method whene the blob columns has null values on db, here is my code :

                  Image img=null; 
                  if(rs.getBinaryStream("ad_photo") != null)  
                      img = new Image(rs.getBinaryStream("ad_photo")); 
                  else 
                      img = new Image("proson.png" );                
                  addadh_adherent_photo.setImage(img);
                  addadh_adherent_photo_label.setText("photo définie");    

and i am getting this exception :

java.lang.NullPointerException

whene the row on db has not a null value of the blob columns all is fine but the problem is whene the row has null value. how can i fix this problem ?