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.
workInProgress.pendingWorkPriority !== NoWork &&
      workInProgress.pendingWorkPriority > renderPriority
    ) {
      
      return;
    }
    
    let newPriority = getUpdatePriority(workInProgress);
    
    let child = workInProgress.child;
    while (child !== null) {
      
      newPriority = largerPriority(newPriority, child.pendingWorkPriority);
      child = child.sibling;
    }
    workInProgress.pendingWorkPriority = newPriority;
  }
  function completeUnitOfWork(workInProgress: Fiber): Fiber | null {
    while (true) {
      
      
      
      
      const current = workInProgress.alternate;
      const next = completeWork(current, workInProgress, nextPriorityLevel);
      const returnFiber = workInProgress.return;
      const siblingFiber = workInProgress.sibling;
      resetWorkPriority(workInProgress, nextPriorityLevel);
      if (next !== null) {
        if (__DEV__) {