Running kplex1.4 on raspbery buster I found the following behavior.
My wind instrument sometimes gives sentences without values like:
MWV,,,,,,A*21 (I know this is weird but...)
This sentence cause an error for kplex like:
ERROR could not convert string to float:
If I define an input filter like the one below there is no more errors and empty value sentences are filtered out in kplex output stream, which at the end is good for me.