Cannot read property 'uid' of null

[mhevery]

function authDataToAuthState(authData, providerData) {
    var uid = authData.uid, providerId = authData.providerData[0].providerId; <<<<<<<<<<<<
    var authState = { auth: authData, uid: uid, provider: null };

EXCEPTION: Error: Uncaught (in promise): EXCEPTION: Error in :0:0
ORIGINAL EXCEPTION: TypeError: Cannot read property 'uid' of null
ORIGINAL STACKTRACE:
TypeError: Cannot read property 'uid' of null
    at Object.authDataToAuthState (http://localhost:4200/vendor/angularfire2/providers/auth_backend.js:30:23)
    at FirebaseSdkAuthBackend.getAuth (http://localhost:4200/vendor/angularfire2/providers/firebase_sdk_auth_backend.js:40:31)
    at AngularFireAuth.getAuth (http://localhost:4200/vendor/angularfire2/providers/auth.js:121:34)
    at new PeriscopeAppComponent (http://localhost:4200/app/periscope.component.js:32:34)
    at DebugAppView._View_PeriscopeAppComponent_Host0.createInternal (PeriscopeAppComponent_Host.template.js:112:38)
    at DebugAppView.AppView.create (http://localhost:4200/vendor/@angular/core/src/linker/view.js:87:21)
    at DebugAppView.create (http://localhost:4200/vendor/@angular/core/src/linker/view.js:299:44)
    at ComponentFactory.create (http://localhost:4200/vendor/@angular/core/src/linker/component_factory.js:147:36)
    at eval (http://localhost:4200/vendor/@angular/core/src/application_ref.js:366:44)
    at eval (http://localhost:4200/vendor/@angular/core/src/application_ref.js:344:26)