[O2-5887] Detect if an empty URL is passed to the CCDB api. (AliceO2Group#14349)

* [O2-5887] Detect if an empty URL is passed to the CCDB api.

* Update testCcdbApi.cxx

Author: Barthelemy

CCDB/src/CcdbApi.cxx

@@ -165,6 +165,10 @@ void CcdbApi::curlInit()
 
 void CcdbApi::init(std::string const& host)
 {
+  if (host.empty()) {
+    throw std::invalid_argument("Empty url passed CcdbApi, cannot initialize. Aborting.");
+  }
+
   // if host is prefixed with "file://" this is a local snapshot
   // in this case we init the API in snapshot (readonly) mode
   constexpr const char* SNAPSHOTPREFIX = "file://";

CCDB/test/testCcdbApi.cxx

@@ -589,4 +589,11 @@ BOOST_AUTO_TEST_CASE(vectored)
   for (auto context : contexts) {
     BOOST_CHECK(context.dest.size() != 0);
   }
-}
+}
+
+BOOST_AUTO_TEST_CASE(empty_url)
+{
+  CcdbApi api;
+  string url = "";
+  BOOST_CHECK_EXCEPTION(api.init(url), invalid_argument, [](std::invalid_argument const&) -> bool { return true; });
+}