Replace a Null Value using TCC during export

Summary

Replace null value with value from another field during TCC Export

Content

Hi all,

I have a TCC export script to extract education details, now in this there are 2 fields one - Institute(a lookup field) second - Other Institute(a text field).

Now during extract I have to write a logic that if lookup field is blank take value from text field else take value from lookup field only. I have written down below logic but it is giving error that it expects a number.
 

<quer:switchByCriterion>

    <quer:cases>

      <quer:case>

        <quer:isTrue>

          <quer:field path="ProfileInformation,Studies,Institution,Description"/>