code: public static @NotNull ImmutableValueMap of(@NotNull String k1, @NotNull Object v1) {
      return new ImmutableValueMap(ImmutableMap.<String, Object>of(k1, v1));
    }
docs: Returns an immutable map containing a single entry. This map behaves and
  performs comparably to {@link Collections#singletonMap} but will not accept
  a null key or value. It is preferable mainly for consistency and
  maintainability of your code.
  @param k1 Key 1
  @param v1 Value 1
  @return ImmutableValueMap