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.
{JSON.stringify(state)}
            </>
          );
        }
      `,
    },
    {
      code: normalizeIndent`
        function Example() {
          const foo = useCallback(() => {
            foo();
          }, []);
        }
      `,
    },
    {
      code: normalizeIndent`
        function Example({ prop }) {
          const foo = useCallback(() => {
            if (prop) {
              foo();
            }
          }, [prop]);
        }
      `,
    },
    {
      code: normalizeIndent`
        function Hello() {
          const [state, setState] = useState(0);