Extract Website Data Using UrlFetchApp.fetch and Regex – Google Sheets

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.