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 = null;
        } catch (e) {
          didError = true;
          error = e;
          continue;
        }
      }
      
      break;
    }
    
    priorityContext = previousPriorityContext;
    
    if (deadline !== null) {
      isCallbackScheduled = false;
    }
    
    if (nextPriorityLevel > TaskPriority && !isCallbackScheduled) {
      scheduleDeferredCallback(performDeferredWork);
      isCallbackScheduled = true;
    }
    const errorToThrow = firstUncaughtError;
    
    isPerformingWork = false;
    deadlineHasExpired = false;
    didFatal = false;
    firstUncaughtError = null;
    capturedErrors = null;
    failedBoundaries = null;
    if (__DEV__) {