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.
static childContextTypes = {message: PropTypes.string};
      static contextTypes = {message: PropTypes.string};
      getChildContext() {
        return {
          message: (this.context.message || '') + this.props.message,
        };
      }
      render() {
        return this.props.children;
      }
    }
    function Connector(props, context) {
      return <span prop={context.message} />;
    }
    Connector.contextTypes = {
      message: PropTypes.string,
    };
    function BadRender() {
      throw new Error('render error');
    }
    class Boundary extends React.Component {
      state = {error: null};
      componentDidCatch(error) {