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.
`useEffect Hook (at line 11) change on every render. ` +
            `To fix this, wrap the definition of 'handleNext' in its own useCallback() Hook.`,
          
          
          suggestions: [
            {
              desc:
                "Wrap the definition of 'handleNext' in its own useCallback() Hook.",
              output: normalizeIndent`
                function MyComponent(props) {
                  let [, setState] = useState();
                  const handleNext = useCallback((value) => {
                    setState(value);
                  });
                  useEffect(() => {
                    return Store.subscribe(handleNext);
                  }, [handleNext]);
                  return <div onClick={handleNext} />;
                }
              `,
            },
          ],
        },
      ],
    },
    {
      code: normalizeIndent`
        function MyComponent(props) {
          function handleNext1() {
            console.log('hello');