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.
},
    {
      code: normalizeIndent`
        function MyComponent({ maybeRef2 }) {
          const definitelyRef1 = useRef();
          const definitelyRef2 = useRef();
          const maybeRef1 = useSomeOtherRefyThing();
          const [state1, setState1] = useState();
          const [state2, setState2] = React.useState();
          const [state3, dispatch1] = useReducer();
          const [state4, dispatch2] = React.useReducer();
          const [state5, maybeSetState] = useFunnyState();
          const [state6, maybeDispatch] = useFunnyReducer();
          const mySetState = useCallback(() => {}, []);
          let myDispatch = useCallback(() => {}, []);
          useEffect(() => {
            // Known to be static
            console.log(definitelyRef1.current);
            console.log(definitelyRef2.current);
            console.log(maybeRef1.current);
            console.log(maybeRef2.current);
            setState1();
            setState2();
            dispatch1();
            dispatch2();
            // Dynamic
            console.log(state1);
            console.log(state2);
            console.log(state3);
            console.log(state4);