code: @SuppressWarnings("unchecked")
      @Override
      public K convertToKey(StreamMessage input) throws ConvertFailException
      {
          K key = null;
  
          try
          {
              key = (K) input.getField(this.keyField);
          }
          catch (Exception ex)
          {
              throw new ConvertFailException(ex);
          }
  
          return key;
      }
docs: {@inheritDoc}