code: @JsonView(EventViews.ContentOnly.class)
      @JsonProperty("content")
      private Map<String, Object> getJsonSerializingContent() {
          //noinspection unchecked
          return (Map<String, Object>) _content;
      }
docs: For purposes of JSON serialization wrapping the content in an unmodifiable view may cause the serializer
  to choose a less-optimal implementation.  Since JSON serialization cannot modify the underlying content
  it is safe to return the original content object to the serializer.