This is a Bug Report

Description

• What went wrong?
  Default variable value not being honored. Throws an error if I run sls deploy without a stage.

• What did you expect should have happened?
  Running sls deploy without --stage option should have set stage to 'development'

• What was the config you used?

provider:
  name: aws
  profile: default
  runtime: nodejs8.10
  stage: ${opt:stage, 'development'}

• What stacktrace or error message from your provider did you see?

Trying to populate non string value into a string for variable ${opt:stage}. Please make sure the value of the property is a string.
Similar or dependent issues:

• Default values don't work in variables within ${file} #5807 (but I'm not importing files, this is just a config within my serverless.yml file)

Additional Data

• Serverless Framework Version you're using: 1.40.0
• Operating System: OSX 10.14.4
• Stack Trace:
• Provider Error messages:
  bbacon@venus (feature/936140__f__create_expired_reserved_holds_lambda *+) ~/dev/clients/dillon/hoopla/hoopla-holds-processing: sls deploy

Serverless Warning --------------------------------------

A valid option to satisfy the declaration 'opt:stage' could not be found.

Serverless Warning --------------------------------------

A valid option to satisfy the declaration 'opt:stage' could not be found.

Serverless Error ---------------------------------------

Trying to populate non string value into a string for variable ${opt:stage}. Please make sure the value of the property is a string.

Get Support --------------------------------------------
Docs: docs.serverless.com
Bugs: github.com/serverless/serverless/issues
Issues: forum.serverless.com

Your Environment Information ---------------------------
OS: darwin
Node Version: 8.11.1
Serverless Version: 1.40.0