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(props) {
          const handleNext1 = () => {
            console.log('hello');
          };
          function handleNext2() {
            console.log('hello');
          }
          useEffect(() => {
            return Store.subscribe(handleNext1);
            return Store.subscribe(handleNext2);
          }, [handleNext1, handleNext2]);
          useEffect(() => {
            return Store.subscribe(handleNext1);
            return Store.subscribe(handleNext2);
          }, [handleNext1, handleNext2]);
        }
      `,
      
      
      
      
      
      errors: [
        {
          message:
            "The 'handleNext1' function makes the dependencies of useEffect Hook " +
            '(at line 12) change on every render. To fix this, wrap the ' +