Update testCcdbApi.cxx

Author: Barthelemy

CCDB/test/testCcdbApi.cxx

@@ -594,6 +594,6 @@ BOOST_AUTO_TEST_CASE(vectored)
 BOOST_AUTO_TEST_CASE(empty_url)
 {
   CcdbApi api;
-  ccdbUrl = "";
-  BOOST_CHECK_EXCEPTION(api.init(ccdbUrl), invalid_argument, [](std::invalid_argument const&) -> bool { return true; });
-}
+  string url = "";
+  BOOST_CHECK_EXCEPTION(api.init(url), invalid_argument, [](std::invalid_argument const&) -> bool { return true; });
+}