code: @SuppressWarnings("rawtypes")
      void addObjectSerializer(final Class c, final ObjectSerializer serializer) {
          _serializers.put(c, serializer);
      }
docs: Assign a ObjectSerializer to perform a type specific serialization scheme
  
  @param c          this object's type serves as a key in the serialization map. ClassMapBasedObjectSerializer uses
  org.bson.util.ClassMap and not only checks if 'c' is a key in the Map, but also walks the up superclass and
  interface graph of 'c' to find matches. This means that it is only necessary assign ObjectSerializers to base
  classes. @see org.bson.util.ClassMap
  @param serializer performs the serialization mapping specific to the @param key type