title: ImmutableMap.of() workaround for HashMap in Maps?
body: <p>There are utility methods to create <code>ImmutableMap</code> like <code>Immutable.of(Key, value)</code> and its overload. <br/><br/>
  But such methods don't exist for <code>HashMap</code> or <code>LinkedHashMap</code> in <code>Maps</code> class. <br/><br/>
  Is there any better way to do this or Guava assumes such a map is always a constant map and <code>ImmutableMap</code> is best option to go with and don't need to provide a utility for <code>HashMap</code>.</p>