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.
const ref = useRef();
                  const [state, setState] = useState();
                  useEffect(() => {
                    ref.current = {};
                    setState(state + 1);
                  }, [ref, state]);
                }
              `,
            },
          ],
        },
      ],
    },
    {
      code: normalizeIndent`
        function MyComponent(props) {
          const ref1 = useRef();
          const ref2 = useRef();
          useEffect(() => {
            ref1.current.focus();
            console.log(ref2.current.textContent);
            alert(props.someOtherRefs.current.innerHTML);
            fetch(props.color);
          }, []);
        }
      `,
      errors: [
        {
          message:
            "React Hook useEffect has missing dependencies: 'props.color' and 'props.someOtherRefs'. " +