SORMAS-Foundation#1613 - Fixed NPE after deleting entity

Author: MateStrysewske

sormas-ui/src/main/java/de/symeda/sormas/ui/utils/AbstractDetailView.java

@@ -70,7 +70,7 @@ protected boolean findReferenceByParams(String params) {
 
 	@Override
 	public void beforeLeave(ViewBeforeLeaveEvent event) {
-		if (subComponent.isDirty()) {
+		if (subComponent != null && subComponent.isDirty()) {
 			showNavigationConfirmPopup(event);
 		} else {
 			event.navigate();