Three points from discussion in https://github.com/reactjs/react-redux/issues/756:

* Due to https://bugs.chromium.org/p/chromium/issues/detail?id=701371, environments like CodeSandbox show `Error: null` in our “React caught an error” warning. Let’s consider skipping both as they’re not very useful and look like a bug. `Error: null` looks like a separate error and draws attention away from the real error just above.

* In any case we should probably not print `The error was thrown at:` if we don’t have a JS stack.

* There is a related issue. What do we pass to error boundary if we caught `null`? It seems that most error boundaries will intuitively do something like `if (this.state.error)` or read `error.message`, which `null` will break. There are other falsy values too like `''` and `undefined`. My proposal is we always wrap primitives into our own `Error` objects that we pass to the boundary.
this.setState({error});
      }
      render() {
        if (this.state.error) {
          return (
            <span prop={`Caught an error: ${this.state.error.message}.`} />
          );
        }
        return this.props.children;
      }
    }
    function BrokenRender(props) {
      throw new Error('Hello');
    }
    ReactNoop.renderToRootWithID(
      <ErrorBoundary>
        <BrokenRender />
      </ErrorBoundary>,
      'a',
    );
    ReactNoop.renderToRootWithID(<span prop="b:1" />, 'b');
    ReactNoop.flush();
    expect(ReactNoop.getChildren('a')).toEqual([
      span('Caught an error: Hello.'),
    ]);
    expect(ReactNoop.getChildren('b')).toEqual([span('b:1')]);
  });
  it('continues work on other roots despite uncaught errors', () => {
    function BrokenRender(props) {