docs: @Override
      protected URL getDefinitionsURL() {
          try {
              URL url = CustomEPSGCodes.class.getResource(CUSTOM_EPSG_CODES_FILE);
              // quickly test url
              try (InputStream stream = url.openStream()) {
                  //noinspection ResultOfMethodCallIgnored
                  stream.read();
              }
              return url;
          } catch (Throwable e) {
              throw new AssertionError("Unable to load /epsg.properties file from root of classpath.");
          }
      }