title: Mule JDBCConnector not setting null values
body: <p>I have configured a JDBConnector which inserts data into a database. The values for the query parameters come from a map returned from a custom transformer. However, even  when the map value is null, Mule returns a NullPayload and the table ends up with nothing in that column.</p>
  
  <pre><code>&lt;jdbc:connector database-ref="myDatasource" ...&gt;
  &lt;jdbc:query key="insertData" value="insert into myTable values(#[message.payload.key])"/&gt;
  &lt;/jdbc:connector&gt;
  </code></pre>
  
  <p>How can I force Mule to insert null when the actual value in the map is null?</p>