When printing to nearest from the HTML5 client, nearest throws a traceback, visible in cups debug output.
> Traceback (most recent call last):
> File "/usr/lib/cups/backend/nearest", line 108, in <module>
> sys . exit ( ooO00oOoo ( ) )
> File "/usr/lib/cups/backend/nearest", line 75, in ooO00oOoo
> if None != get_terminal_hfolder ( Ooo0 , oO0O ) :
> File "/opt/thinlinc/modules/thinlinc/tlprinter.py", line 361, in get_terminal_hfolder
> for O0OO0O in generate_alternative_hwaddrs ( hwaddr ) :
> File "/opt/thinlinc/modules/thinlinc/tlprinter.py", line 318, in generate_alternative_hwaddrs
> assert None != i11Iii , "Require internal hardware address format"
> AssertionError: Require internal hardware address format
Somewhere along the way an empty hardware address gets turned into the string "unknown", which doesn't match the regexp used in the generate_alternative_hwaddrs function.