title: How to avoid null values serialization in HashMap?
body: <p>I would like to serialize a HashMap as a string through the Jackson JSON processor.
  For example:</p>
  
  <pre><code>String strMap = getMapper().writeValueAsString(myHashMap);
  result output -&gt; {"r_id":6,"a_am":null,"smb":"Submit","a_li":null,"l_id":878,"pos":[1345,1346,1347]}
  </code></pre>
  
  <p>I don't know how to disable null values serialization for Map. It works fine only for POJO if configure the Jackson like this:</p>
  
  <pre><code>mapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);
  </code></pre>