code: @Override
      public String serialize(final FedoraEvent evt) {
          try {
              return MAPPER.writeValueAsString(from(evt));
          } catch (final JsonProcessingException ex) {
              LOGGER.error("Error processing JSON: {}", ex.getMessage());
              return null;
          }
      }
docs: Serialize a FedoraEvent into a JSON String
  @param evt the Fedora event
  @return a JSON string