Runaway Promises on session.writeTransaction()

When using the Bluebird package as a the global Promise engine, I keep on getting Runaway Promise warning on session.writeTransaction(). I have recently upgraded from Neo4j v3.5 to v4.0, so I had to upgrade the Neo4j driver as well. This issue does not occur with session.run() nor with session.beginTransaction().

System Info

• Neo4j version: Enterprise 4.0.0
• Neo4j Mode: Single instance
• Driver version: Javascript lanaguage driver 4.0.1
• Operating system: Ubuntu 18.04 on local machine (laptop)
• Bluebird.js version: 3.5.5

Steps to reproduce

1. Start the dockerized Neo4j conrainer
2. Setup a Node.js server
3. Install Bluebird.js and use it as the global promise engine (instructions on their website)
4. Install the Neo4j javascript driver v4.0.1
5. Run a MERGE/SET query with the session.writeTransaction() function

Stacktrace

Warning: a promise was created in a handler at domain.js:131:23 but was not returned from it, see http://goo.gl/rRqMUw at Promise.then (<redacted>/node_modules/bluebird/js/release/promise.js:154:17)

[Kefa7y]

@martin-neotech We are actually returning results from our functions. Furthermore, this issue only appeared when upgrading to the neo4j js driver v4.0.1. It used to work just fine without errors for multiple older driver versions.

Here is a (slightly modified) code snippet that is pulled from our code:

function getUserCount() {
  const session = driver.session();
  const statement = `
    MATCH (user: User)
    RETURN COUNT(user)`;

  return session
    .readTransaction((tx) => tx.run(statement))
    .then((result) => {
      session.close();
      const count = result.records[0]._fields[0];
      return count;
    })
    .finally(() => session.close());
}

As you can see, we do not leave runaway promises with our code, not even in insert functions. I firmly believe that this is an issue in the driver itself that started with the v 4.x updates. Could you please investigate into the matter?

[timsaval]

@lutovich thank you either way!