al-if question

Hi,

this may be a stupid question, but I'm new to Albatross
and didn't find a solution in the documenation. How
can check with al-if, wether a variable is defined or not?
When I try a <al-if expr="bla"> and bla is not defined I
get an error....NameError: name 'bla' is not defined
But I need something like this, because the variable
will be defined later.

Thanks,
Axel

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