Undefined output

Vault
1 
    apiVersion: 'v1', // default
    endpoint: 'http://127.0.0.1:8200', // default
    token: 's.AtNGE1eiqZXl06DtZWnMUMVZ' // optional client token; can be fetched after valid initialization of the server
  };
   var vault = require("node-vault")(options);

   vault.write('secret/bar6', {value : 'world6' , lease : '1h'}).then( (result) =>{
       console.log("write", result)
   }).catch(err => console.log("err", err))

output : write undefined

data write successfully but still, I always get undefined output.
can anyone simplify this.