Error `Cannot read property 'commandsTakeWriteConcern' of null` in v4.6.0

On the line mongoose.connection.db.dropDatabase( done ); We are getting the error

Cannot read property 'commandsTakeWriteConcern' of null
      at decorateWithWriteConcern (/redacted/node_modules/mongoose/node_modules/mongodb/lib/db.js:485:36)
      at Db.dropDatabase (/redacted/node_modules/mongoose/node_modules/mongodb/lib/db.js:872:3)
      at Array.db.dropDatabase (/redacted/src/db/index.js:20:25)
      at node_modules/async/lib/async.js:596:38
      at _arrayEach (node_modules/async/lib/async.js:85:13)
      at Object.async.auto (node_modules/async/lib/async.js:554:9)
      at Context.<anonymous> (test/config.js:25:9)

However the version mongoose@4.5.9 works fine.

Thanks in advance

[ct5845]

I had the same issue. I got it working by changing where i had my drop statement to;

mongoose.connection.once('connected', () => {
    mongoose.connection.db.dropDatabase();
});

[vkarpov15]

Use this instead:

mongoose.connection.dropDatabase(error => {
  console.log('Error', error);
  process.exit(0);
});

The way we fixed this issue was adding a dropDatabase helper in mongoose that ties in with mongoose’s buffering.