public static <T, U> Pair<T, U> pair(T left, U right) {
      return new Pair<>(left, right);
    }
the query map will be generated using member variable names as query parameter names.

<p>eg: "/uri?name={name}&number={number}"

<p>order of included query parameters not guaranteed, and as usual, if any value is null, it will
be left out
core/src/main/java/feign/querymap/FieldQueryMapEncoder.java