Conditions in mail signatures

How can I output a content including the variable only if the condition is that the user variable is used or populated.

Like if else…

Example: (syntax I stole from another programming language).
{if condition=user.phone}Phone: #{user.phone}{/if}

Zammad variables and Zammad in general do not support conditional variables.
I think there’s a feature request living some where on this board for that.