fix(tracing): trace hook error out when see nil

[StarlightIbuki]

Summary

"instrument" hooks toip, db_connect and other functions that widely used by core and plugins, and collect data for tracing.

I surprisingly find the hooking function will error out when set_attribute got a nil value. For example, A failing DNS query would emit an error with traceback: "invalid value".

This will definitely change the behavior of the hooked function. toip would have returned (nil, err) if it's not hooked, but instead, it throws an error and the error has nothing to do with the origin error. This could cause more serious issues for other hooked functions.

Luckily, we do not have more cases where set_attributes receives invalid values.

The complete list of hooked functions will be shown offline.

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG

N/A There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Full changelog

• Change "error" to "log".

Issue reference

KAG-749

[fffonion]

seems the failing test is related

[StarlightIbuki]

seems the failing test is related

It is. But let's wait until the 3.2 released

[StarlightIbuki]

I tried reverting the change and the test still fails for t/01-pdk/08-response/11-exit.t (39, 41, 42, 43).
The master is not red. No idea why it fails at this branch.