Check if a key is in gun.js

For example, before I put something in the database I want to check if that entry is already there.
I try to do this:

gun.get('demograph').once((data, key) => {
  console.log("realtime updates 1:", data);
});

but I didn’t get a response if ‘demograph’ is or not in the database( for example to get true or false) I just get the result.

I also tried to use .not from extensible API but I is not working.
Anyone has any idea how to check if an entry is already in the database?

>Solution :

I’m not a user of Gun but from what I see in the doc https://gun.eco/docs/API#-a-name-get-a-gun-get-key-
get allows a second argument callback where you can test for not found

gun.get(key, function(ack){
  if(ack.err){
    server.log(error)
  } else
  if(!ack.put){
    // not found
  } else {
    // data!
  }
})