title: how can I filter map entries based on set of entries
body: <p>I'm using google guava 12 and have a map:</p>
  
  <pre><code>Map&lt;OccupancyType, BigDecimal&gt; roomPrice;
  </code></pre>
  
  <p>I have a Set:</p>
  
  <pre><code>Set&lt;OccupancyType&gt; policy;
  </code></pre>
  
  <p>How can I filter entries in the <code>roomPrice map</code> based on <code>policy</code> and return the filtered map ?</p>
  
  <p><code>filteredMap</code> needs to have all the values from <code>policy</code>. In case, roomPrice map doesnt have an entry from policy, I'd like to input default value instead.</p>