Using UrlFetchApp.fetch(url) with regex to extract website data

I'm trying to extract data from a list of >1000 URLs using a script that uses UrlFetchApp.fetch(url) and regex based on this article.

This is the code I'm using.

function importRegex(url, regex_string) {  var html, content = '';  var response = UrlFetchApp.fetch(url);  if (response) {    html = response.getContentText();    if (html.length && regex_string.length) {      var regex = new RegExp( regex_string, "i" );      content = html.match(regex)[1];    }  }  content = unescapeHTML(content);  Utilities.sleep(1000); // avoid call limit by adding a delay  return content;  }var htmlEntities = {  cent:  '¢',  pound: '£',  yen:   '¥',  euro:  '€',  copy:  '©',  reg:   '®',  lt:    '<',  gt:    '>',  mdash: '–',  quot:  '"',  amp:   '&',  apos:  '\''};function unescapeHTML(str) {    return str.replace(/\&([^;]+);/g, function (entity, entityCode) {        var match;        if (entityCode in htmlEntities) {            return htmlEntities[entityCode];        } else if (match = entityCode.match(/^#x([\da-fA-F]+)$/)) {            return String.fromCharCode(parseInt(match[1], 16));        } else if (match = entityCode.match(/^#(\d+)$/)) {            return String.fromCharCode(~~match[1]);        } else {            return entity;        }    });};

and the importregex function formula I'm using is

=importRegex(A4, "<h1 class=""ch-title"".*?>(.*)<\/h1>")

It gives the following error

TypeError: Cannot read property '1' of null (line 9).

I'm not sure how to fix it.