Looks like the check for duplicate switch doesn't ignore blank switches.
local(external.add_external_network)> set net_addr "LXD containers"
local(external.add_external_network)> set net_addr <ADDR>/24
local(external.add_external_network)> set description "LXD containers"
local(external.add_external_network)> execute
Error: Switch of that name already exists
Looks like the check for duplicate switch doesn't ignore blank switches.