title: Is it possible to make json4s not to throw exception when required field is missing?
body: <p>Is it possible to make json4s not to throw exception when required field is missing ?</p>
  
  <p>When I "extract" object from raw json string it throws exception like this one</p>
  
  <pre><code>org.json4s.package$MappingException: No usable value for pager
  No usable value for rpp
  Did not find value which can be converted into byte
      at org.json4s.reflect.package$.fail(package.scala:98)
      at org.json4s.Extraction$ClassInstanceBuilder.org$json4s$Extraction$ClassInstanceBuilder$$buildCtorArg(Extraction.scala:388)
      at org.json4s.Extraction$ClassInstanceBuilder$$anonfun$11.apply(Extraction.scala:396)
  </code></pre>
  
  <p>Is it possible just to let it be null ?</p>