I tried this for an var marked as "UNDEF" in log

<condition field="${var}" expression="^UNDEF$" break="never">

<condition field="${var}" expression="UNDEF" break="never">

<condition field="${var}" expression="undef" break="never">

<condition field="${var}" expression="^undef$" break="never">

<condition field="${var}" expression="" break="never">

<condition field="${var}" expression="^$" break="never">

<condition field="${var}" expression="[UNDEF]" break="never">

<condition field="${var}" expression="[]" break="never">

without success.

which is the right expression for empty var please ?

Thanks