Fixes NullPointerException for contacts that don't have preferred protocol provider.

src/net/java/sip/communicator/service/gui/UIContactDetail.java

@@ -172,7 +172,9 @@ public Iterator<String> getLabels()
     public ProtocolProviderService getPreferredProtocolProvider(
         Class<? extends OperationSet> opSetClass)
     {
-        return preferredProviders.get(opSetClass);
+        if (preferredProviders != null)
+            return preferredProviders.get(opSetClass);
+        return null;
     }
 
     /**
@@ -203,7 +205,9 @@ public void addPreferredProtocolProvider(
      */
     public String getPreferredProtocol(Class<? extends OperationSet> opSetClass)
     {
-        return preferredProtocols.get(opSetClass);
+        if (preferredProtocols != null)
+            return preferredProtocols.get(opSetClass);
+        return null;
     }
 
     /**