shallow wrapper instance is null

```jsx
import React from 'react';
import { BrowserRouter } from "react-router-dom";
import { Provider } from "react-redux";
import { shallow } from 'enzyme';
import renderer from "react-test-renderer";

import Logout from './Logout';
import mockStore from "../../../../test/mockStoreHelper";

describe('', () => {
const defaultProps = {
actions: { signOut: jest.fn() },
history: { push: jest.fn() },
};
const renderShallow = (props = {}) =>
shallow((





));

it('renders', () => {
const jsonTree = renderer
.create(renderShallow())
.toJSON();

expect(jsonTree).toMatchSnapshot();
});

it('checks redirectLogin', () => {
const wrapper = renderShallow();
const instance = wrapper.instance();

instance.redirectLogin();

expect(defaultProps.actions.signOut).toBeCalled();
expect(defaultProps.history.push).toBeCalledWith('/login');
});
});
```

### Current behavior
I'm getting this error - TypeError: Cannot read property 'redirectLogin' of null
Instance is always null

### Your environment
Windows

#### API

- [ ] shallow

#### Version

| library | version
| ------------------------------| -------
| enzyme | 3.9.0
| enzyme-adapter-react-16 | 1.12.1
| react | 16.8.4
| react-dom | 16.8.4
| react-test-renderer | 16.8.6

#### Adapter

- [ ] enzyme-adapter-react-16

Run the shown Logout test and inspect ./Logout together with the renderShallow helper and test/mockStoreHelper. Check how the shallow wrapper is created around Provider and BrowserRouter, then verify the expected redirectLogin behavior and assertions after identifying the cause of the null instance.

Written by the indexing model from the issue text.