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.
var getComponentName = require('getComponentName');
var {createWorkInProgress, largerPriority} = require('ReactFiber');
var {onCommitRoot} = require('ReactFiberDevToolsHook');
var {
  NoWork,
  SynchronousPriority,
  TaskPriority,
  HighPriority,
  LowPriority,
  OffscreenPriority,
} = require('ReactPriorityLevel');
var {AsyncUpdates} = require('ReactTypeOfInternalContext');
var {
  PerformedWork,
  Placement,
  Update,
  PlacementAndUpdate,
  Deletion,
  ContentReset,
  Callback,
  Err,
  Ref,
} = require('ReactTypeOfSideEffect');
var {
  HostRoot,
  HostComponent,
  HostPortal,
  ClassComponent,
} = require('ReactTypeOfWork');
var {getUpdatePriority} = require('ReactFiberUpdateQueue');