How to create a balancer instance in apisix 3.3.0?

[Jingzhenzxz]

OS: win 10

APISIX: 3.3.0-debian

etcd: bitnami/etcd:3.4.15

Docker Desktop version: 4.20.1

I want to use balancer to modify the upstream address of the request.

gray_release plugin is:

local core = require("apisix.core")
local json = require("apisix.core.json")
local balancer = require("apisix.balancer")

local plugin_name = "gray_release"

local _M = {
    version = 0.1,
    priority = 1000,
    type = 'rewrite',
    name = plugin_name,
    schema = {
        type = "object",
        properties = {}
    },
}


function _M.check_schema(conf)
    core.log.warn("Enter the check schema stage")
    return core.schema.check(_M.schema, conf)
end

function _M.rewrite(conf, ctx)
            local new_upstream = {
                type = 'roundrobin',
                nodes = {["127.0.0.1" .. ":" .. 8080] = 1},
            }

            local checker = ctx.up_checker
            local server_picker, err = balancer.create_server_picker(new_upstream, checker)
            
            if not server_picker then
                core.log.warn("failed to create server picker: ", err)
                return 503, "failed to create new server picker"
            end
end

return _M

The route I created is:

{
    "uri": "/",
    "plugins": {
        "gray_release": {}
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:8081": 1
        }
    },
    "pass_host": "node",
    "scheme": "https"
}

When I visit 127.0.0.1:9080, the apisix container prints such a line of logs:

[error] 60#60: *2347 lua entry thread aborted: runtime error: /usr/local/apisix/apisix/plugins/gray_release.lua:125: attempt to call field 'create_server_picker' (a nil value)

How can I correctly create a balancer instance?

If you need other information, please let me know, thank you!

I tried to replace "create_server_picker" with "new" method, apisix will print a similar log:
attempt to call field 'new' (a nil value).