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.
errors: [
        {
          message:
            'React Hook useEffect has unnecessary dependencies: ' +
            "'MutableStore.hello.world', 'global.stuff', and 'z'. " +
            'Either exclude them or remove the dependency array. ' +
            "Outer scope values like 'MutableStore.hello.world' aren't valid dependencies " +
            "because mutating them doesn't re-render the component.",
          
          
          suggestions: [
            {
              desc: 'Update the dependencies array to be: [props.foo, x, y]',
              output: normalizeIndent`
                import MutableStore from 'store';
                let z = {};
                function MyComponent(props) {
                  let x = props.foo;
                  {
                    let y = props.bar;
                    useEffect(() => {
                      // nothing
                    }, [props.foo, x, y]);
                  }
                }
              `,
            },
          ],
        },
      ],