Maven resolving missing envvar to its name

Question

inside properties I have:

<myvar>${env.MY_VAR}</myvar>

if env.MY_VAR is set to 'abc'   then myvar is resolved to 'abc'

if env.MY_VAR is not set    then myvar is resolved to '${env.MY_VAR}'

the same is true when I try to use ${env.MY_VAR} directly anywhere in the pom
The problem is that this way I can't use the property or envvar when I want to conditionaly check whether it is set or not, because it is always set.

Why is that? how can I just have a null/emptystring when envvar is not set?