Filtering on empty elements

[mchccc]

I'm quietly exploring this great tool, and I found myself stuck on filtering empty elements.
I'm using pyShark, and I don't seem able to use the filter string as I do using Wireshark's GUI: some protocols create tree items only if needed, and sometimes the information inside those branches is not as meaningful as the branch's existence itself.
Is it possible to filter such information? Or to modify the code in order to reach it.. I'm still unsure whether it's a technical difficulty or if it simply isn't implemented yet, so I thought I'd ask.
Thanks a lot for the great work.