p:if 029 (AB)

The pipeline

<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error" xmlns:p="http://www.w3.org/ns/xproc" xmlns:xs="http://www.w3.org/2001/XMLSchema" version="3.0">
   <p:output port="result"/>
   <p:identity>
      <p:with-input>
         <doc/>
      </p:with-input>
   </p:identity>
   <p:if test="/doc" collection="{true()}">
      <p:identity>
         <p:with-input>
            <doc2/>
         </p:with-input>
      </p:identity>
   </p:if>
</p:declare-step>