code: @Nullable
      private static String paramName(String token) {
          if (token.startsWith("{") && token.endsWith("}")) {
              return token.substring(1, token.length() - 1);
          }
  
          if (token.startsWith(":")) {
              return token.substring(1);
          }
  
          return null;
      }
docs: Returns the name of the path parameter contained in the path element. If it contains no path parameter,
  {@code null} is returned. e.g.
  <ul>
  <li>{@code "{foo}"} -> {@code "foo"}</li>
  <li>{@code ":bar"} -> {@code "bar"}</li>
  <li>{@code "baz"} -> {@code null}</li>
  </ul>