Zendesk code: TypeError: null is not an object (evaluating 'e.contentDocument')

[sentry-io[bot]]

Sentry Issue: MICROMASTERS-2H5

TypeError: null is not an object (evaluating 'e.contentDocument')
  at None (./static/js/entry/zendesk_widget.js:154:26)
  at promiseReactionJob ([native code])

[alicewriteswrongs]

happens here in entry/zendesk_widget.js:

        // and the changes we make will be visible to the user.
        wait(100).then(() => {
          const ticketIFrame = document.querySelector(
            "iframe.zEWidget-ticketSubmissionForm"
          )
          const select = ticketIFrame.contentDocument.querySelector("select")
          const optionValues = _.map(select.options, "value")
          if (optionValues.includes(programSlug)) {
            select.value = programSlug
          }
        })

I suspect that sometimes wait(100) just isn't long enough to ensure that the iframe has been created yet. We should either set up something to retry or we should catch this error and silence it.