The sender PID of the notification was being set to the target PID,
instead of the sender PID. Use correct PID and remove redundant target
PID argument.
Also fix minor accuracy issues.
Now database getters do error handling aswell, and in case of any error,
the NEX or GRPC method throws a proper error about it.
There are still some doubts on how to handle errors when a list of data
is processed, so for now skip that element on the list and continue.
Also add some constant errors to do better error handling.
