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`
        const MyComponent = forwardRef((props, ref) => {
          useImperativeHandle(ref, () => ({
            focus() {
              alert(props.hello);
            }
          }), [props.hello])
        });
      `,
    },
    {
      
      
      
      code: normalizeIndent`
        function MyComponent(props) {
          let obj = someFunc();
          useEffect(() => {
            obj.foo = true;
          }, [obj]);
        }
      `,
    },
    {
      code: normalizeIndent`
        function MyComponent(props) {
          let foo = {}