Cannot read property 'length' of null

[vaikutin]

Hi,
I installed and run "node server.js". It looks fine but when I tried to connect from a web browser.
It shows the following error message and crash.
Please help me to figure out what is wrong.
Thank you.

events.js:174
      throw er; // Unhandled 'error' event
      ^

TypeError: Cannot read property 'length' of null
    at /home/bitnami/src/classes/AppRouter.js:65:33
    at /home/bitnami/node_modules/mongoose/lib/query.js:3122:9
    at process._tickCallback (internal/process/next_tick.js:68:7)
Emitted 'error' event at:
    at Immediate.<anonymous> (/home/bitnami/node_modules/mongoose/lib/query.js:3128:23)
    at runCallback (timers.js:705:18)
    at tryOnImmediate (timers.js:676:5)
    at processImmediate (timers.js:658:5)