code: @SuppressWarnings("rawtypes")
      public Object getField(String key)
      {
          if (this.body == null || Map.class.isAssignableFrom(this.body.getClass()) == false)
          {
              return null;
          }
  
          return ((Map) this.body).get(key);
      }
docs: Get field from message body.
  
  @param key key
  @return field mapped key