Reason for sox mix restriction to two or more input files?

Dear all,


I am using sox for automatic, scripted file generation.

One step is a mix of several input files.  It may happen
that - by configuration - only a single input file remains
for that mixing step.

This cannot be handled by sox, because sox _requires_
at least two input files and quits with the message
   "Not enough input filenames specified"

I understand that at least one input file is necessary
(for finding the target length, sample rate etc.), but
why does sox fail when mixing a single input file?


          Best regards,

                   Thomas