Whenever we sort a set of records with NULL key 
automatically it consider the records as one group & data 
will be as per the input serial number and will be sorted 
according to that.But dedup will again cosider the records 
as one group &  output will be the first record 
automatically.
e.g.input records:1,XYZ,100;
                  2,ABC,700;
                  5,JJJ,400;
                  7,KKK,500;
 using NULL key sort component will give output as:
                  1,XYZ,100;
                  2,ABC,700;
                  5,JJJ,400;
                  7,KKK,500;
Dedup sort will give output as:
                  1,XYZ,100;

i think in the above case dedup sort will give all the
records in out put even if we sort on any of the three 
fields