fix(handleRef): handle null ref correctly

[layershifter]

A small fix for the handleRef ref utility.

typeof null // "object"

There is a similar condition in React's code: https://github.com/facebook/react/blob/e58ecda9a2381735f2c326ee99a1ffa6486321ab/packages/react-reconciler/src/ReactFiberCommitWork.js#L625

[layershifter]

Should I add a record to CHANGELOG.md for this?

[codecov]

Codecov Report

Merging #487 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #487   +/-   ##
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  Coverage   88.42%   88.42%           
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  Files          42       42           
  Lines        1451     1451           
  Branches      186      186           
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  Hits         1283     1283           
  Misses        163      163           
  Partials        5        5

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[layershifter]

The easiest case if when we will try use cloneElement and try to catch a component's ref:

const htmlInput = <input />

// ----

cloneElement(htmlInput, {
  ref: (node) => {
    // 1. Calling existing handler
    // A. We need to keep user's behaviour working, for example for 3rd party libs
    // B. `ref` is not a prop in React, so when `ref` is not passed it's `null` by default 
    //     and here it will fail without this fix
    handleRef(child.ref, node)
    // 2. Calling our handler
    this.handleInputRef(node)
  }
})

So, this fix is for a handler ref, not for a value.