‘attempt to call a nil value’ error

[suikabreaker]

2021/08/31 11:00:21 [error] 124259#0: *1 lua entry thread aborted: runtime error: /usr/local/restywaf/site/lualib/resty/waf.lua:258: attempt to call a nil value
stack traceback:
coroutine 0:
    /usr/local/restywaf/site/lualib/resty/waf.lua: in function '_process_rule'
    /usr/local/restywaf/site/lualib/resty/waf.lua:481: in function 'exec'
    access_by_lua(nginx.conf:51):20: in main chunk, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "localhost:8060"
2021/08/31 11:00:21 [error] 124259#0: *1 failed to run header_filter_by_lua*: /usr/local/restywaf/site/lualib/resty/waf.lua:59: attempt to call a nil value
stack traceback:
    /usr/local/restywaf/site/lualib/resty/waf.lua:59: in function '_parse_collection'
    /usr/local/restywaf/site/lualib/resty/waf.lua:226: in function '_process_rule'
    /usr/local/restywaf/site/lualib/resty/waf.lua:481: in function 'exec'
    header_filter_by_lua:8: in main chunk, client: 127.0.0.1, server: , request: "GET / HTTP/1.1", host: "localhost:8060"

#user  nobody;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;

events {
    worker_connections  1024;
}

http {
    init_by_lua_block {
        -- use resty.core for performance improvement, see the status note above
        require "resty.core"

        -- require the base module
        local lua_resty_waf = require "resty.waf"

        -- perform some preloading and optimization
        lua_resty_waf.init()
    }
    server {
        listen       8060;
        location / {
            access_by_lua_block {
                local lua_resty_waf = require "resty.waf"

                local waf = lua_resty_waf:new()

                -- define options that will be inherited across all scopes
                waf:set_option("debug", false)
                waf:set_option("mode", "ACTIVE")
                waf:set_option("event_log_level", ngx.WARN)

                -- this may be desirable for low-traffic or testing sites
                -- by default, event logs are not written until the buffer is full
                -- for testing, flush the log buffer every 5 seconds
                --
                -- this is only necessary when configuring a remote TCP/UDP
                -- socket server for event logs. otherwise, this is ignored
                waf:set_option("event_log_periodic_flush", 5)

                -- run the firewall
                waf:exec()
            }

            header_filter_by_lua_block {
                local lua_resty_waf = require "resty.waf"

                -- note that options set in previous handlers (in the same scope)
                -- do not need to be set again
                local waf = lua_resty_waf:new()

                waf:exec()
            }

            body_filter_by_lua_block {
                local lua_resty_waf = require "resty.waf"

                local waf = lua_resty_waf:new()

                waf:exec()
            }

            log_by_lua_block {
                local lua_resty_waf = require "resty.waf"

                local waf = lua_resty_waf:new()

                waf:write_log_events()
            }

            proxy_pass http://192.168.120.250:8100;
        }
    }
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
    #                  '$status $body_bytes_sent "$http_referer" '
    #                  '"$http_user_agent" "$http_x_forwarded_for"';

    #access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    #gzip  on;
}

openresty: https://openresty.org/download/openresty-1.19.3.2.tar.gz install thought opm

I don't know weither is it because of opm or lua-resty-waf. I've tried to debug and found that operator REFIND causes the problem, which is not found in operators.lua. It seems like code and rule is not compatible to echo other.