Onion support in dnsmasq

I have added these lines to dnsmasq for onion support on router level.

  option rebind_localhost '1'
    list rebind_domain '/.onion/'

and it works.
but then luci dnsmasq section
192.168.1.1/cgi-bin/luci/admin/network/dhcp
will show the "Domain whitelist" with /.onion/ in red and when saving it it says
" One or more fields contain invalid values!"

what should I do to fix this?

I dont understand. I have read that part of config.
but how that helps me?
I used my config and dnsmasq works. as in it correctly assigns local ips to onion domains.
and using /onion/ doesnt work( it still says error).

dnsmasq deosnt have a problem with my config.
luci configuration page has a problem with it.

You can file an issue here:
https://github.com/openwrt/luci/issues

Have you tried list rebind_domain '/onion/'?

yes.
I have tested with many things.
the luci pages doesnt even accept /.com/ I think it only accepts full domains.

AFAIK the slashes are NOT required for a single domain and just onion is accepted by luci. I don't have TOR set up, but If I were you I'd try that.

pkease read my first post.
my issue is this: dnsmasq accepts ".com" for all domains that have. com suffix.
i use this to whitelist ".onion" domains.
now luci 18.04 doesnt accepts that with or without "/"

p.s.
I installed 19.07 version of luci and this bug is gone.