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.
error = event.error;
        didSetError = true;
      }
      
      const evtType = `react-${name ? name : 'invokeguardedcallback'}`;
      
      window.addEventListener('error', onError);
      fakeNode.addEventListener(evtType, callCallback, false);
      
      
      const evt = document.createEvent('Event');
      evt.initEvent(evtType, false, false);
      fakeNode.dispatchEvent(evt);
      if (didError) {
        if (!didSetError) {
          
          error = new Error(
            'An error was thrown inside one of your components, but React ' +
              "doesn't know what it was. This is likely due to browser " +