Ionic2 : Uncaught (in promise): invalid link: calendar - ionic2

Question

I have implemented a side-menu in Ionic2.I am getting "Invalid link" when i click on the Event or Map button on the side-menu and sometimes i get the error as "Invalid Views to insert". I tried removing quotes from the calendar and gmap but it does not work out.
Please guide.
This is my TS file:
import { Component } from '#angular/core';
import { Platform , IonicPage } from 'ionic-angular';
import { StatusBar } from '#ionic-native/status-bar';
import { SplashScreen } from '#ionic-native/splash-screen';
import { CalendarPage } from '../pages/calendar/calendar'
import { GmapPage } from '../pages/gmap/gmap'
import firebase from 'firebase';
import { LoginPage } from '../pages/login/login';
import { ViewChild } from '#angular/core';
import { NavController } from 'ionic-angular/navigation/nav-controller';
import { AuthProvider } from '../providers/auth/auth';
#IonicPage()
#Component({
templateUrl: 'app.html'
})
export class MyApp {
calendar: CalendarPage;
gmap: GmapPage;
#ViewChild('nav') nav: NavController;
rootPage: any = CalendarPage;
pages = []
constructor(platform: Platform, statusBar: StatusBar, splashScreen:SplashScreen,
public authProvider: AuthProvider) {
platform.ready().then(() => {
// Okay, so the platform is ready and our plugins are available.
// Here you can do any higher level native things you might need.
statusBar.styleDefault();
splashScreen.hide();
const unsubscribe = firebase.auth().onAuthStateChanged(user => {
if (!user) {
this.rootPage = 'LoginPage';
unsubscribe();
} else {
this.rootPage = 'EventPage';
unsubscribe();
}
});
});
}
onLoad(page : string) {
this.nav.setRoot(page);
}
onLogout(){
this.authProvider.logoutUser();
}
}
This is my HTML code :
<ion-menu [content] = "nav">
<ion-header>
<ion-toolbar>
<ion-title>Menu</ion-title>
</ion-toolbar>
</ion-header>
<ion-content>
<ion-list>
<button ion-item (click) = "onLoad('calendar')">Events</button>
<button ion-item (click) = "onLoad('gmap')">Maps</button>
<button ion-item (click) = "onLogout()">Logout</button>
</ion-list>
</ion-content>
</ion-menu>
<ion-nav [root]="rootPage" #nav></ion-nav>