title: "??" operator in TypeScript
body: <p>I have following code:</p>
  <pre><code>const helperText = fieldError ?? !salesforceLink ? t('editEstimate.reviewInformation.mandatoryFieldsError') : '';
  </code></pre>
  <p>Can anybody exmplain me or event send a link what <code>??</code> is?</p>