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.
"definition of 'handleNext1' in its own useCallback() Hook.",
          suggestions: [
            {
              desc:
                "Wrap the definition of 'handleNext1' in its own useCallback() Hook.",
              output: normalizeIndent`
                function MyComponent(props) {
                  const handleNext1 = useCallback(() => {
                    console.log('hello');
                  });
                  function handleNext2() {
                    console.log('hello');
                  }
                  useEffect(() => {
                    return Store.subscribe(handleNext1);
                    return Store.subscribe(handleNext2);
                  }, [handleNext1, handleNext2]);
                  useEffect(() => {
                    return Store.subscribe(handleNext1);
                    return Store.subscribe(handleNext2);
                  }, [handleNext1, handleNext2]);
                }
              `,
            },
          ],
        },
        {
          message:
            "The 'handleNext2' function makes the dependencies of useEffect Hook " +
            '(at line 12) change on every render. To fix this, wrap the ' +