Fixed service discovery

src/main/java/org/gcube/gcat/client/GCatClientDiscovery.java

@@ -77,7 +77,9 @@ public class GCatClientDiscovery {
 		try {
 			SimpleQuery proxyQuery = queryForProxy(GCatConstants.SERVICE_CLASS);
 			addresses = ICFactory.client().submit(proxyQuery);
-			
+			if(addresses==null || addresses.isEmpty()){
+				throw new Exception("No ResourceRegistry Proxy Found");
+			}
 		} catch (Exception e) {
 			logger.debug("{}. Looking for RunningInstance.", e.getMessage());
 			SimpleQuery serviceQuery = queryForService(GCatConstants.SERVICE_CLASS);