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.
return function(arg) {
        if (map.has(arg)) {
          
          
          return map.get(arg);
        }
        const result = fn(arg);
        map.set(arg, result);
        return result;
      };
    }
    /**
     * Visitor for both function expressions and arrow function expressions.
     */
    function visitFunctionWithDependencies(