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.
if (this.state.error) {
          return <span prop={this.state.error.message} />;
        }
        return this.props.children;
      }
    }
    const InvalidType = undefined;
    function BrokenRender(props) {
      return <InvalidType />;
    }
    ReactNoop.render(
      <ErrorBoundary>
        <BrokenRender />
      </ErrorBoundary>,
    );
    ReactNoop.flush();
    expect(ReactNoop.getChildren()).toEqual([
      span(
        'Element type is invalid: expected a string (for built-in components) or ' +
          'a class/function (for composite components) but got: undefined. ' +
          "You likely forgot to export your component from the file it's " +
          'defined in.\n\nCheck the render method of `BrokenRender`.',
      ),
    ]);
    expect(console.error.calls.count()).toBe(1);
  });
  it('catches reconciler errors in a boundary during update', () => {
    spyOn(console, 'error');
    class ErrorBoundary extends React.Component {