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.
"React Hook useEffect has unnecessary dependencies: 'ref1.current' and 'ref2.current'. " +
            'Either exclude them or remove the dependency array. ' +
            "Mutable values like 'ref1.current' aren't valid dependencies " +
            "because mutating them doesn't re-render the component.",
          suggestions: [
            {
              desc: 'Update the dependencies array to be: [activeTab]',
              output: normalizeIndent`
                function MyComponent({ activeTab }) {
                  const ref1 = useRef();
                  const ref2 = useRef();
                  useEffect(() => {
                    ref1.current.scrollTop = 0;
                    ref2.current.scrollTop = 0;
                  }, [activeTab]);
                }
              `,
            },
          ],
        },
      ],
    },
    {
      code: normalizeIndent`
        function MyComponent({ activeTab, initY }) {
          const ref1 = useRef();
          const ref2 = useRef();
          const fn = useCallback(() => {
            ref1.current.scrollTop = initY;
            ref2.current.scrollTop = initY;