asterisk users - Dec 2011 - AEL2: How get rid of "expression has operators, but no variables" warnings

Hi,

I'm converting an existing dialplan written in AEL2 to Asterisk 1.8.
While at it, I'm trying to get rid of some AEL2 warnings messages that
used to clutter my console when loading AEL scripts.

Specifically, my dialplan includes this simple text assignment :
prefix1="FooBar => ";

It produces this:
 expression "FooBar => " has operators, but no variables.
Interesting...

Using Set application makes it but I would appreciate an other way to do it.
Suggestion ?

Regards