fix(ssr): fix window references

src/@ionic-native/core/decorators/common.ts

@@ -149,7 +149,11 @@ function wrapObservable(pluginObj: any, methodName: string, args: any[], opts: a
  * @returns {Observable}
  */
 function wrapEventObservable(event: string, element: any): Observable<any> {
-  element = element ? get(window, element) : window;
+  if (typeof window !== 'undefined') {
+    element = element && typeof window !== 'undefined' ? get(window, element) : window;
+  } else {
+    element = element || {};
+  }
   return fromEvent(element, event);
 }
 
@@ -307,8 +311,11 @@ export function callInstance(
 }
 
 export function getPlugin(pluginRef: string): any {
+  if (typeof window !== 'undefined') {
     return get(window, pluginRef);
   }
+  return null;
+}
 
 export function get(element: Element | Window, path: string) {
   const paths: string[] = path.split('.');

src/@ionic-native/core/ionic-native-plugin.ts

@@ -26,8 +26,11 @@ export class IonicNativePlugin {
    * Returns the original plugin object
    */
   static getPlugin(): any {
+    if (typeof window !== 'undefined') {
       return get(window, this.pluginRef);
     }
+    return null;
+  }
 
   /**
    * Returns the plugin's name