Don't force flexform data for pi2
pi2 (the PDF-Icon) checks if there are flexform data available and throws an error if not.
That prevents me from using it like this:
lib.toolsnavigation.20 =< plugin.tx_pdfcontroller_pi2
I think it's not unusual to include the button via TypoScript or Fluid-Template and NOT as a CE.
For now I will create a CE and render it using a RECORD query, but that's not a nice way to include the Icon.