I'm using thinky#2.3.6 and that pulled down rethinkdbdash#2.3.21. I only ran into this when I started to use the pingInterval option.

Here's the full error:

(node:46024) Warning: a promise was created in a handler at `node_modules/rethinkdbdash/lib/pool.js:248:14` but was not returned from it, see http://goo.gl/rRqMUw
      at new Promise (`./node_modules/rethinkdbdash/node_modules/bluebird/js/release/promise.js:77:14`)

To fix it, I put in return statements at the line specified above, and also on line: 321. Not sure that is the correct fix though, so I haven't created a PR.