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 {
      isUsed: false, 
      isSatisfiedRecursively: false, 
      isSubtreeUsed: false, 
      children: new Map(), 
    };
  }
  
  
  dependencies.forEach((_, key) => {
    const node = getOrCreateNodeByPath(depTree, key);
    node.isUsed = true;
    markAllParentsByPath(depTree, key, parent => {
      parent.isSubtreeUsed = true;
    });
  });
  
  
  declaredDependencies.forEach(({key}) => {
    const node = getOrCreateNodeByPath(depTree, key);
    node.isSatisfiedRecursively = true;
  });
  stableDependencies.forEach(key => {
    const node = getOrCreateNodeByPath(depTree, key);
    node.isSatisfiedRecursively = true;
  });
  
  function getOrCreateNodeByPath(rootNode, path) {