addNewTag

// your version

@RequestMapping(value="/addNewTag", method=RequestMethod.POST, produces = "application/json")
@ResponseBody
public Map<String, Integer> addNewTag(@RequestBody Map<String, String> requestMap, HttpServletResponse response) throws IOException {
    if (addTagOnRuntime(requestMap.get("tagName"))) {
        return Collections.singletonMap("statusCode", HttpServletResponse.SC_OK);
    } else {
        response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        return null;
    }
}

private boolean addTagOnRuntime(String tagName) {
    tagsAddedOnRuntime.add(tagName);
    return true;
}

// my version
@RequestMapping(value="/addNewTag", method=RequestMethod.POST, produces = "application/json")
@ResponseBody
public void addNewTag(@RequestBody String newTag) throws IOException {
    tagsAddedOnRuntime.add(newTag);
}