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 function Counter() {
            let [count, setCount] = useState(0);
            useEffect(() => {
              let id = setInterval(() => {
                setCount(count => count + increment);
              }, 1000);
              return () => clearInterval(id);
            }, []);
            return <h1>{count}</h1>;
          }
        }
      `,
    },
    {
      code: normalizeIndent`
        function App() {
          const [query, setQuery] = useState('react');
          const [state, setState] = useState(null);
          useEffect(() => {
            let ignore = false;
            fetchSomething();
            async function fetchSomething() {
              const result = await (await fetch('http://hn.algolia.com/api/v1/search?query=' + query)).json();
              if (!ignore) setState(result);
            }
            return () => { ignore = true; };
          }, [query]);
          return (
            <>
              <input value={query} onChange={e => setQuery(e.target.value)} />