code: @Nullable
      static String getString(
              @NonNull JSONObject jsonObject,
              @NonNull @Size(min = 1) String fieldName) throws JSONException {
          return nullIfNullOrEmpty(jsonObject.getString(fieldName));
      }
docs: Calls through to {@link JSONObject#getString(String)} while safely
  converting the raw string "null" and the empty string to {@code null}.
  
  @param jsonObject the input object
  @param fieldName the required field name
  @return the value stored in the requested field
  @throws JSONException if the field does not exist