"nvram boot-args" returns error

It would appear that as default serverperfmode=1 is not set, therefore rather than it being serverperfmode=0 it literally does not exist.

The error message you are getting is consistent I believe with not having any boot-args set at all. I get this on my OS X Servers as well. I do however get the following on my OS X clients.

sh-3.2# nvram boot-args

boot-args mbasd=1

This is what I would expect in our circumstances, the above enables support for the USB Apple SuperDrive and is an option I have enabled on all our clients as part of the imaging process I use.

You might want to see Turn on performance mode for OS X Server - Apple Support

Based on its wording I interpret it also as confirming that the default is that Performance mode is not enabled.

I came across this thread after reading the linked article and getting the same error. And I can confirm that going ahead and issuing the command to turn on performance mode made it so the error was not returned when nvram boot-args was issued.

I provided feedback on the article because I thought it could be clearer.

I suppose you are using macOS Sierra. According to this Apple support document, starting with macOS Sierra, you must be booted to the recovery partition to run the nvram command.