Filtering Radius Attributes by length

Hello,

I am trying to discover any Radius attributes that don't have a specific length. I have discovered that I can show all packets containing a specific attribute with a filter like this:

radius.3Com_Connect_Id

but any attempt to perform further filtering based on the length of such an attribute proves fruitless i.e.

radius.3Com_Connect_Id.len >= 0

presents me with an empty window.

I have been looking at the documentation here: https://www.wireshark.org/docs/dfref/r/radius.html

Am I misunderstanding the role of this '.len' suffix, or am I using it incorrectly?

Thanks and Best Regards, Robert