bug: version apisix3.9 ,dashboard version 3.0.1,The console displays an exception.

[1450793561]

Current Behavior

According to this official documenthttps://apisix.apache.org/zh/docs/apisix/3.9/plugins/proxy-rewrite/, when you use the header.add interface to add something, it will be displayed in the console like this:

Use the following call interface parameters.

`{
"uri": "/111111*",
"upstream_id": "web",
"hosts": [
"abc12.com"
],
"name": "111111",
"desc": "1111111n",
"plugins": {
"response-rewrite": {
"headers": {
"Cache-Control": "$cache"
}
},
"proxy-rewrite": {
"headers":{
"add": {
"Host": "$host",
"X-Real-IP": "$remote_addr",
"X-Forwarded-For": "$proxy_add_x_forwarded_for"
}
}

    }
},
"timeout": {
    "connect": 3,
    "send": 3,
    "read": 3
}

}`

Expected Behavior

No response

Error Logs

No response

Steps to Reproduce

`{
"uri": "/111111*",
"upstream_id": "sign-web",
"hosts": [
"abc12.com"
],
"name": "111111",
"desc": "1111111n",
"plugins": {
"response-rewrite": {
"headers": {
"Cache-Control": "$cache"
}
},
"proxy-rewrite": {
"headers":{
"add": {
"Host": "$host",
"X-Real-IP": "$remote_addr",
"X-Forwarded-For": "$proxy_add_x_forwarded_for"
}
}

    }
},
"timeout": {
    "connect": 3,
    "send": 3,
    "read": 3
}

}`

Environment

• APISIX version (run apisix version):
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):