sun.reflect.GeneratedMethodAccessorxx.invoke(Unknown Source) in StackTrace

I am trying to get information from the stack trace like this

StackTraceElement element = Thread.currentThread().getStackTrace()[3];

But in the log I can see following: sun.reflect.GeneratedMethodAccessor42.invoke(Unknown Source) fileName: null, method: invoke

Can you please tell me why the Unknown Source? Is it due to the reflection? compiler? The runtime? Something else?

Thank you