Loggly error without adding loggly plugin

Hi, everyone. I got below errors even without adding any loogly plugin. I’m using a pretty old kong verion 0.14.1, have many clusters using kong, but only one of them has this problem.

Appreciate if anyone provides insightful ideas! thanks!

2022/03/15 07:45:22 [error] 22265#0: *334672873 lua entry thread aborted: runtime error: /usr/local/share/lua/5.1/kong/plugins/loggly/handler.lua:86: attempt to compare two nil values
stack traceback:
coroutine 0:
    /usr/local/share/lua/5.1/kong/plugins/loggly/handler.lua: in function </usr/local/share/lua/5.1/kong/plugins/loggly/handler.lua:85>, context: ngx.timer, client:, server: