0 or other falsy but non-nullish values being ignored for certain key properties

[noinkling]

Bug Report

Using falsy checks for keys in certain places means we're unable to use 0 (and possibly false, NaN, etc.) as a key. In #1729 the resolution seemed to be to use nullish semantics, but at least a few components didn't get the memo:

Semantic-UI-React/src/views/Feed/Feed.js

Line 37 in 694e399

const finalKey = childKey || [date, meta, summary].join('-')

Semantic-UI-React/src/views/Item/ItemGroup.js

Line 52 in 694e399

childKey ||

Semantic-UI-React/src/modules/Search/Search.js

Line 414 in 694e399

key={childKey || result.id || result.title}

Semantic-UI-React/src/views/Card/CardGroup.js

Line 63 in c828368

const key = item.key || [item.header, item.description].join('-')

I was going to open a PR fixing these cases to use Lodash's isNil() as elsewhere, however I was thinking now that the nullish coalescing operator (??) is part of JS, maybe you guys would like to add the Babel plugin for it so we could use that instead? I notice that the optional chaining plugin is already there.

Edit: I just realized that nullish coalescing is probably already available from preset-env.

Steps

e.g:

const items = [
  { childKey: 0, content: 'Foo' },
  { childKey: 1, content: 'Bar' }
];
<Item.Group items={items} />

Expected Result

The generated Items should have a key of "0" and "1" respectively.

Actual Result

The first item has a generated key based on its other props: "Foo---"

Version

2.0.1

Testcase

Directly from one of the doc examples: https://codesandbox.io/s/tooji?module=/example.js

[layershifter]

Was fixed in semantic-ui-react@2.0.3 🎉