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.
nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
            
            
            
            
            if (nextUnitOfWork === null) {
              invariant(
                pendingCommit !== null,
                'Should have a pending commit. This error is likely caused by ' +
                  'a bug in React. Please file an issue.',
              );
              
              
              if (deadline.timeRemaining() > timeHeuristicForUnitOfWork) {
                priorityContext = TaskPriority;
                commitAllWork(pendingCommit);
                priorityContext = nextPriorityLevel;
                
                handleCommitPhaseErrors();
                
                if (
                  nextPriorityLevel === NoWork ||
                  nextPriorityLevel > minPriorityLevel ||
                  nextPriorityLevel < HighPriority
                ) {
                  
                  break;
                }
              } else {
                deadlineHasExpired = true;