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.
stopFailedWorkTimer(node);
        }
        break;
      } else if (__DEV__) {
        stopWorkTimer(node);
      }
      node = node.return;
    }
  }
  function scheduleRoot(root: FiberRoot, priorityLevel: PriorityLevel) {
    if (priorityLevel === NoWork) {
      return;
    }
    if (!root.isScheduled) {
      root.isScheduled = true;
      if (lastScheduledRoot) {
         
        lastScheduledRoot.nextScheduledRoot = root;
        lastScheduledRoot = root;
      } else {
         
        nextScheduledRoot = root;
        lastScheduledRoot = root;
      }
    }
  }
  function scheduleUpdate(fiber: Fiber, priorityLevel: PriorityLevel) {
    if (__DEV__) {
      recordScheduleUpdate();