Liquid: How to handle null in result of fetchXML

{% fetchxml my_query %}
<fetch version="1.0" output-format="xml-platform" mapping="logical" distinct="false" returntotalrecordcount="true">
.....
.....
<filter type="and">
        <condition attribute="asc_id" operator="eq" uitype="new_uitype" value="{{request.params.id}}" />
      </filter>
    </link-entity>
  </entity>
</fetch>

{% if my_query.results.entities %}
  {{ my_query.results.entities.size }}
{% else %}
  <span class="alert">No session found for this booking</span>
{% endif %}

Liquid error: Exception has been thrown by the target of an invocation.