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 value = useMemo(() => { return 2*2; });
          const fn = useCallback(() => { alert('foo'); });
        }
      `,
      
      errors: [
        {
          message:
            'React Hook useMemo does nothing when called with only one argument. ' +
            'Did you forget to pass an array of dependencies?',
          suggestions: undefined,
        },
        {
          message:
            'React Hook useCallback does nothing when called with only one argument. ' +
            'Did you forget to pass an array of dependencies?',
          suggestions: undefined,
        },
      ],
    },
    {
      
      code: normalizeIndent`
        function MyComponent({ fn1, fn2 }) {
          const value = useMemo(fn1);
          const fn = useCallback(fn2);