Unable to change knobs when following CONTRIBUTING guidelines for reproducing a bug

[kmurgic]

Describe the bug
This may just be missing information in the CONTRIBUTING.md file, but I followed the steps in the CONTRIBUTING.md for reproductions. I opened the /examples/official-storybook folder and ran storybook, and got an error when trying to change a knob. I am seeing an error that the dotenv file is not loaded, not sure if this is related, but guessing that it is unrelated.

This may just be an issue of needing more documentation in the CONTRIBUTING.md - is there an extra step that needs to be taken to use addons?

To Reproduce
Steps to reproduce the behavior:

1. git clone https://github.com/storybookjs/storybook.git
2. cd storybook
3. yarn bootstrap --core2. Click on '....'
4. cd examples/official-storybook
5. yarn storybook
6. open the story addons -> knobs -> withknobs -> select-knob
7. try to change the value knob
8. get an error message (see below) and the value doesn't change

Expected behavior
A clear and concise description of what you expected to happen.
The knob changes and the corresponding value changes

** Screenshots **

Code snippets
If applicable, add code samples to help explain your problem.

TypeError: Cannot set property 'value' of undefined
    at Object.knobChanged (registerKnobs.js:38)
    at index.js:188
    at Array.forEach (<anonymous>)
    at Channel.handleEvent (index.js:187)
    at PostmsgTransport.<anonymous> (index.js:77)
    at PostmsgTransport.handler (index.js:126)
    at PostmsgTransport.handleEvent (index.js:300)
error @ index.js:60

System
Please paste the results of npx sb@next info here.

Additional context
Add any other context about the problem here.