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.
}
describe('react-hooks', () => {
  const parserOptions = {
    ecmaFeatures: {
      jsx: true,
    },
    ecmaVersion: 6,
    sourceType: 'module',
  };
  const testsBabelEslint = {
    valid: [...testsFlow.valid, ...tests.valid],
    invalid: [...testsFlow.invalid, ...tests.invalid],
  };
  new ESLintTester({
    parser: require.resolve('babel-eslint'),
    parserOptions,
  }).run('parser: babel-eslint', ReactHooksESLintRule, testsBabelEslint);
  new ESLintTester({
    parser: require.resolve('@babel/eslint-parser'),
    parserOptions,
  }).run(
    'parser: @babel/eslint-parser',
    ReactHooksESLintRule,
    testsBabelEslint
  );
  const testsTypescriptEslintParser = {
    valid: [...testsTypescript.valid, ...tests.valid],
    invalid: [...testsTypescript.invalid, ...tests.invalid],
  };
  new ESLintTester({