title: Is there a way to inverse/inverse an ImmutableMap
body: <p>Given an <code>ImmutableMap&lt;K,V&gt;</code> where values are non-unique, is there a way to invert / inverse / pivot this to an ImmutableMap like collection that allows for multiple keys?</p>
  
  <p>I would assume that it would end up being an <code>ImmutableSetMultiMap&lt;V,K&gt;</code></p>
  
  <p>I was previously using an <code>ImmutableSetMultiMap&lt;K,V&gt;</code> but realized that it allowed multiple keys, which could be a possible source of bugs in the future.</p>
  
  <p>This also renders a ImmutableBiMap useless, as there could be non-unique values.</p>