Set Variable if Current Field is Empty

Question

I'm trying to set a variable within my templates which does the following:

If this field is empty then use another field instead.

I have 2x Fields called affiliateUrl and offerLink, if offerLink is empty, then use the affiliateUrl instead.

The current code I'm running is this:

{% set affiliateLink = relatedEntry.offerLink ? relatedEntry.affiliateLink : relatedEntry.affiliateUrl %}

Error Code:

Calling unknown method: craft\elements\Entry::affiliateLink()

The rest of the code is below:

        {% set affiliateLink = relatedEntry.offerLink ? relatedEntry.affiliateLink : relatedEntry.affiliateUrl %}


        {% if relatedEntry.offerCode is empty %}
          <div class="utility-vertical-align">
            <a href="{{ affiliateLink }}" target="_blank" class="btn btn-voucher btn-lg btn-block">Get This Offer<i class="material-icons float-sm-right">chevron_right</i></a>
          </div>
        {% else %}
          <div class="utility-vertical-align">
            <pre>
                window.aPopunder = [
                    ['{{ relatedEntry.offerLink }}']
                ];
            </pre>
            <a href="{{ relatedEntry.url }}" target="_blank" class="btn btn-voucher btn-lg btn-block" onclick="$.popunder(this);">Reveal Code & Visit<i class="material-icons">chevron_right</i></a>
          </div>
        {% endif %}

Answer 1

Required a different operator

{% set affiliateLink = relatedEntry.offerLink ?? relatedEntry.affiliateUrl %}