No boot-args in nvram
This is indeed the normal response if the variable has not been set.
Example commands and output along your line of inquiry:

$ nvram boot-args
  boot-args serverperfmode=1 -v


Whereas:

$ nvram bootargs        # missing character results in: non existing variable
  nvram: Error getting variable - 'bootargs': (iokit/common) data was not found


This is the same state for this variable you get after deleting the whole variable or after clearing all variables with an NVRAM reset. 

And if nvram -p does show nothing but what you posted then such a procedure was quite recent.

To test for 'normality':

$ nvram -p                        # print all nvram variables
boot-args serverperfmode 1 -v     # output if only boot-args is set
$ sudo nvram -d boot-args         # delete nvram variable for boot-args
$ nvram -p                        # print all nvram variables
                                  # nothing to output
$ nvram boot-args                 # try to read only boot-args variable 
nvram: Error getting variable - 'boot-args': (iokit/common) data was not found # your error message
$ sudo nvram boot-args="-v"       # set boot-args to verbose boot mode
$ nvram -p                        # print all nvram variables
boot-args -v                      # output for nvram variable boot-args shown
$ nvram boot-args                 # print only boot-args nvram variable
boot-args -v