**Do you want to request a *feature* or report a *bug*?**
Bug

**What is the current behavior?**
Page load throws console error: `Warning: Stateless function components cannot be given refs. Attempts to access this ref will fail.null`

```
// Chrome console
6VM598:27 Warning: Stateless function components cannot be given refs. Attempts to access this ref will fail.null
window.console.error @ VM598:27
printWarning @ warning.js:36
warning @ warning.js:60
mountIndeterminateComponent @ react-dom.development.js:10488
beginWork @ react-dom.development.js:10647
performUnitOfWork @ react-dom.development.js:12621
workLoop @ react-dom.development.js:12730
callCallback @ react-dom.development.js:1319
invokeGuardedCallbackDev @ react-dom.development.js:1358
invokeGuardedCallback @ react-dom.development.js:1215
performWork @ react-dom.development.js:12848
batchedUpdates @ react-dom.development.js:13292
performFiberBatchedUpdates @ react-dom.development.js:1666
stackBatchedUpdates @ react-dom.development.js:1657
batchedUpdates @ react-dom.development.js:1671
batchedUpdatesWithControlledComponents @ react-dom.development.js:1684
dispatchEvent @ react-dom.development.js:1894
```

**What is the expected behavior?**
No console error. Or at least some way to trace which is the stateless component that is causing the issue.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
`"react": "^16.0.0-rc.3",`
`Chrome Version 60.0.3112.113 (Official Build) (64-bit)`
`macOS Sierra 10.12.6`


- This error only started to appear after upgrading from React 15 -> 16.
};
exports.resetContext = function(): void {
  previousContext = emptyObject;
  contextStackCursor.current = emptyObject;
  didPerformWorkStackCursor.current = false;
};
exports.findCurrentUnmaskedContext = function(fiber: Fiber): Object {
  
  
  invariant(
    isFiberMounted(fiber) && fiber.tag === ClassComponent,
    'Expected subtree parent to be a mounted class component. ' +
      'This error is likely caused by a bug in React. Please file an issue.',
  );
  let node: Fiber = fiber;
  while (node.tag !== HostRoot) {
    if (isContextProvider(node)) {
      return node.stateNode.__reactInternalMemoizedMergedChildContext;
    }
    const parent = node.return;
    invariant(
      parent,
      'Found unexpected detached subtree parent. ' +
        'This error is likely caused by a bug in React. Please file an issue.',
    );
    node = parent;
  }
  return node.stateNode.context;
};