v5.1.x change breaks Boolean knob

Describe the bug Changing value to value: value || '' in addons/knobs/src/components/PropForm.js (introduced with bug fix #6043 😞 ) causes boolean knobs to return an empty string when toggled from true, which itself causes the error:

Warning: Failed prop type: Invalid prop `knob.value` of type `string` supplied to `BooleanType`, expected `boolean`.

To Reproduce Steps to reproduce the behavior:

1. Go an existing project with a Boolean knob
2. in node_modules/@storybook/addon-knobs/dist/components/PropForm.js around line 76 change value: value || '' to just value (broken to fixed) or vice versa.
3. Restart the server (e.g. yarn storybook)
4. With console log open, toggle a boolean knob

Expected behavior Toggling a boolean from true should not result in an error about an empty string.

Screenshots

Bad === value: value || ''

Good === value === value: value,

Code snippets

  _createClass(PropForm, [{
    key: "makeChangeHandler",
    value: function makeChangeHandler(name, type) {
      var onFieldChange = this.props.onFieldChange;
      return function (value) {
        var change = {
          name: name,
          type: type,
          // value,            // <-- GOOD in v5.0.6
          value: value || '',  // <-- BROKEN in v5.1.x
        };
        onFieldChange(change);
      };
    }
  }, {

i.e. the opposite of bugfix #6043

Additional context This boolean bug was introduced in a fix for changing a number value to an empty value (#6043). Fixes should account for both scenarios.

[leoyli]

I think I can fix this when in the upcoming weekend 😃

[metasean]

@leoyli - No sweat from my end. If my pile hadn’t been so high (and remained so high) I would have submitted a PR instead of a just a bug report. So at this point, I’m just happy you’ve submitted a fix! Thank you! 🙇‍♂️