[fix] do not crash if publication date is missing in pubmed engine

                    content = content[0:300] + "..."

        # TODO: center snippet on query term

        publishedDate = datetime.strptime(entry.xpath('.//DateCreated/Year')[0].text

                                          + '-' + entry.xpath('.//DateCreated/Month')[0].text

                                          + '-' + entry.xpath('.//DateCreated/Day')[0].text, '%Y-%m-%d')

        res_dict = {'url': url,

                    'title': title,

                    'publishedDate': publishedDate,

                    'content': content}

        try:

            publishedDate = datetime.strptime(entry.xpath('.//DateCreated/Year')[0].text

                                              + '-' + entry.xpath('.//DateCreated/Month')[0].text

                                              + '-' + entry.xpath('.//DateCreated/Day')[0].text, '%Y-%m-%d')

            res_dict['publishedDate'] = publishedDate

        except:

            pass

        results.append(res_dict)

        return results