eslint-plugin-react-hooks version: 4.2.0

## Steps To Reproduce

I know it shouldn't exist in production code, but it's annoying while editing some files.

```js
import React, { useEffect } from "react";

const App = () => {
  useEffect(); // <-
  return null;
};

export default App;
```

Link to code example: https://codesandbox.io/s/polished-sun-3wr27?file=/src/App.js

## The current behavior

ESLint crashed.

```
TypeError: Cannot read property 'type' of undefined
```

## The expected behavior

ESLint doesn't crash but reports an error instead.
return (
    typeof val === 'object' &&
    val !== null &&
    !Array.isArray(val) &&
    typeof val.type === 'string'
  );
}
function isSameIdentifier(a, b) {
  return (
    (a.type === 'Identifier' || a.type === 'JSXIdentifier') &&
    a.type === b.type &&
    a.name === b.name &&
    a.range[0] === b.range[0] &&
    a.range[1] === b.range[1]
  );
}
function isAncestorNodeOf(a, b) {
  return a.range[0] <= b.range[0] && a.range[1] >= b.range[1];
}