v1.34.4: fix optional<Json> return to avoid implicit conversion warnings

Author: GaspardKirira

include/vix/json/json.hpp

@@ -127,7 +127,12 @@ namespace vix::json
    * Json j = R"({"a": 1, "b": 2})"_json;
    * @endcode
    */
-  namespace literals = nlohmann::literals;
+#if defined(NLOHMANN_JSON_VERSION_MAJOR)
+#if (NLOHMANN_JSON_VERSION_MAJOR > 3) || \
+    (NLOHMANN_JSON_VERSION_MAJOR == 3 && NLOHMANN_JSON_VERSION_MINOR >= 10)
+  namespace literals = nlohmann::literals::json_literals;
+#endif
+#endif
 
 } // namespace vix::json
 

include/vix/json/loads.hpp

@@ -145,7 +145,8 @@ namespace vix::json
   {
     try
     {
-      return Json::parse(s);
+      Json j = Json::parse(s);
+      return j;
     }
     catch (...)
     {