TypeError: bucketName.charAt is not a function

[itsmepetrov]

In our project we specify buckets via Ref:

events:
  - s3:
      existing: true
      bucket: !Ref IndexBucket
      rules:
        - prefix: data/batch/

unfortunately it breaks getResourceForBucket function:

error - unhandledRejection: TypeError: bucketName.charAt is not a function
    at ServerlessS3Local.getResourceForBucket (.../node_modules/serverless-s3-local/index.js:509:8)

I've created PR that resoles the issue: #947