code: @Nullable
      static Map<String, Object> optMap(
              @NonNull JSONObject jsonObject,
              @NonNull @Size(min = 1) String fieldName) {
          JSONObject foundObject = jsonObject.optJSONObject(fieldName);
          if (foundObject == null) {
              return null;
          }
  
          return jsonObjectToMap(foundObject);
      }
docs: Calls through to {@link JSONObject#optJSONObject(String)} and then
  uses {@link #jsonObjectToMap(JSONObject)} on the result.
  
  @param jsonObject the input object
  @param fieldName the required field name
  @return the value stored in the requested field, or {@code null} if the key is not present