In Kamailio config I use empty globalĀ string variable
local.trace_troubleshooting_net = "" descr "trace all SIP messages from given network"

When I check variable value I get blank string
kamcmd cfg.get local trace_troubleshooting_net

I can set new value
[root@host]# kamcmd cfg.sets local trace_troubleshooting_net "2600::/48"
[root@host]# kamcmd cfg.get local trace_troubleshooting_net
2600::/48

Now I want to set the empty customĀ  global variable using a command
kamcmd cfg.sets group trace_troubleshooting_net ""
But get error
error: 400 - error at parameter 2: expected string type but record doesn't match type

How to properly set empty values?