public boolean equals(Object o) {
        if (!(o instanceof DocumentUpdateResponse)) {
            return false;
        }

        DocumentUpdateResponse docResp = (DocumentUpdateResponse) o;

        return super.equals(docResp) && ((documentUpdate == null && docResp.documentUpdate == null) || (
                documentUpdate != null && docResp.documentUpdate != null &&
                        documentUpdate.equals(docResp.documentUpdate)));
    }
Returns the document update of this response or null if there is none

@return the DocumentUpdate, or null
documentapi/src/main/java/com/yahoo/documentapi/DocumentUpdateResponse.java