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.
if (
    (node.parent.type === 'MemberExpression' ||
      node.parent.type === 'OptionalMemberExpression') &&
    node.parent.object === node &&
    node.parent.property.name !== 'current' &&
    !node.parent.computed &&
    !(
      node.parent.parent != null &&
      (node.parent.parent.type === 'CallExpression' ||
        node.parent.parent.type === 'OptionalCallExpression') &&
      node.parent.parent.callee === node.parent
    )
  ) {
    return getDependency(node.parent);
  } else if (
    
    node.type === 'MemberExpression' &&
    node.parent &&
    node.parent.type === 'AssignmentExpression' &&
    node.parent.left === node
  ) {
    return node.object;
  } else {
    return node;