[gPXE] fall-back filename

[Alexander Heinz]

> In the meanwhile, you could have a look at including "lib.gpxe"[1] at
> the top of your script, then using the '${if1}', '${if2}', '${if3}' and
> '${cond}' items to accomplish your conditional choice.

Maybe I misunderstood some parts of lib.gpxe because I cannot answer the 
following question myself. If I try to do

${take} ${filename}

and the variable filename is not set (because the DHCP server does not 
provide this option), I get the following error:
Syntax: set <identifier> <value>

and the script execution aborts.

However ${take} ${filename} works if filename is not empty.

So is there another way to do this?

Best regards,
Alex