automatic key name

[duz17]

what is the key string that created automatically for declaring new preference (without specifying it)?
var useTestAutoCapture: Boolean by bindToPreferenceField(false)

I know I could put it like this and have it:
var useTestAutoCapture: Boolean by bindToPreferenceField(false, "useTestAutoCapture")

but let's say I didn't, released a version and need to know this string (to use in preferences activity for example)

I couldn't find the answer for it, even on debug