code: public Map<String, Object> getHeaders() {
          Map<String, Object> map = new HashMap<>();
          map.put("Content-length", "0");
          map.put(CONTENT_TYPE, contentType);
          map.put("Accept", "application/json");
          for (Map.Entry<String, Object> entry : extraHeaders.entrySet()) {
              map.put(entry.getKey(), entry.getValue());
          }
          return map;
      }
docs: Builds the headers to be passed in the HTTP call
  
  @return Map: a mapping of the headers in key to values