Gemplus 8kb Combi Card

how can i get the mifare key of Gemplus 8kb Combi Card?

coding:
System.out.println("Waiting for a card..");
terminal.waitForCardPresent (0);
Card card = terminal.connect("T=0");

output:
after i run this coding.the error is detect.
Waiting for a card..
java.lang.NullPointerException
at my.xx.xxx.Read.<init>(Read.java:34)
i used gemplus 8kb combicard..and creader is omnikey 5321.
the protocol i used is correct but stil the data from the card cannot be displayed.does anyone know?