If your files are stored with a mode lower than 0644, AWS Lambda won't execute and will report the errors below.

If you execute the function with the "Test" button from the Lambda console:

{
  "errorMessage": "callback called with Error argument, but there was a problem while retrieving one or more of its message, name, and stack"
}

and, in CloudWatch Logs:
module initialization error: Error

The current workaround is to chmod a+r -Rv . in your project's root folder.