added null check to avoid npe when choosing to show recipients before doing choices

src/main/java/se/su/dsv/scipro/admin/panels/AdminMailPanel.java

@@ -235,6 +235,7 @@ public class AdminMailPanel extends Panel {
 	private void showRecipients(){
 		ArrayList<String> mailList = new ArrayList<String>();
 		for(User u : userSet){
+			if (u!=null)
 			mailList.add(u.toString() + " (" + u.getEmailAddress() +")");
 		}
 		Collections.sort(mailList);