Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in.

Check the render method of `Navigator`.

instantiateReactComponent
    instantiateReactComponent.js:88:8
instantiateChild
    ReactChildReconciler.js:57:53
traverseAllChildrenImpl
    traverseAllChildren.js:84:6
instantiateChildren
    ReactChildReconciler.js:88:8
_reconcilerInstantiateChildren
    ReactMultiChild.js:180:12
mountChildren            
    ReactMultiChild.js:250:6
initializeChildren
    ReactNativeBaseComponent.js:67:41
mountComponent
    ReactNativeBaseComponent.js:169:6
mountComponent
    ReactReconciler.js:58:6
performInitialMount
    ReactCompositeComponent.js:519:6
mountComponent
    ReactCompositeComponent.js:350:8
mountComponent
    ReactReconciler.js:58:6
updateChildren
    ReactChildReconciler.js:165:10
_reconcilerUpdateChildren
    ReactMultiChild.js:212:10
_updateChildren
    ReactMultiChild.js:353:6
updateChildren
    ReactMultiChild.js:339:25
receiveComponent
    ReactNativeBaseComponent.js:119:24
receiveComponent
    ReactReconciler.js:159:38
_updateRenderedComponentWithNextElement
    ReactCompositeComponent.js:1129:8
_updateRenderedComponent
    ReactCompositeComponent.js:1100:6
_performComponentUpdate
    ReactCompositeComponent.js:1036:36
updateComponent
    ReactCompositeComponent.js:921:8
receiveComponent
    ReactCompositeComponent.js:753:6
receiveComponent
    ReactReconciler.js:159:38
updateChildren
    ReactChildReconciler.js:144:10
_reconcilerUpdateChildren
    ReactMultiChild.js:212:10
_updateChildren
    ReactMultiChild.js:353:6
updateChildren
    ReactMultiChild.js:339:25
receiveComponent
    ReactNativeBaseComponent.js:119:24
receiveComponent
    ReactReconciler.js:159:38
_updateRenderedComponentWithNextElement
    ReactCompositeComponent.js:1129:8
_updateRenderedComponent
    ReactCompositeComponent.js:1100:6
_performComponentUpdate
    ReactCompositeComponent.js:1036:36
updateComponent
    ReactCompositeComponent.js:921:8
receiveComponent
    ReactCompositeComponent.js:753:6
receiveComponent
    ReactReconciler.js:159:38
_updateRenderedComponentWithNextElement
    ReactCompositeComponent.js:1129:8
_updateRenderedComponent
    ReactCompositeComponent.js:1100:6
_performComponentUpdate
    ReactCompositeComponent.js:1036:36
updateComponent
    ReactCompositeComponent.js:921:8
performUpdateIfNecessary
    ReactCompositeComponent.js:778:8
performUpdateIfNecessary
    ReactReconciler.js:209:46
runBatchedUpdates
    ReactUpdates.js:150:6
perform
    Transaction.js:149:24
perform
    Transaction.js:149:24
flushBatchedUpdates
    ReactUpdates.js:168:24
closeAll
    Transaction.js:222:29
perform
    Transaction.js:163:24
batchedUpdatesWithControlledComponents
    ReactGenericBatching.js:51:26
_receiveRootNodeIDEvent
    ReactNativeEventEmitter.js:111:40
receiveTouches
    ReactNativeEventEmitter.js:200:8
__callFunction
    MessageQueue.js:244:47
<unknown>
    MessageQueue.js:108:26
guard
    MessageQueue.js:46:4
callFunctionReturnFlushedQueue
    MessageQueue.js:107:10