请教：安装好lua-resty-checkups后使用openresty测试readme中的demo始终报attempt to index field 'checkups' (a nil value)

[ttany]

如图，经过无数次的验证，无法解决：
2018/12/21 14:24:30 [error] 58540#0: *280 lua entry thread aborted: runtime error: /usr/local/lib/lua/resty/checkups/api.lua:65: attempt to index field 'checkups' (a nil value)
stack traceback:
coroutine 0:
/usr/local/lib/lua/resty/checkups/api.lua: in function 'ready_ok'

[samuelyao314]

lua_code_cache on; 就没有这个错误了