3 files changed, 20 insertions, 7 deletions
diff --git a/Timeline/ClientApp/src/app/utilities/debounce-click.directive.spec.ts b/Timeline/ClientApp/src/app/utilities/debounce-click.directive.spec.ts
index 75710d0c..89f66b99 100644
--- a/Timeline/ClientApp/src/app/utilities/debounce-click.directive.spec.ts
+++ b/Timeline/ClientApp/src/app/utilities/debounce-click.directive.spec.ts
@@ -13,8 +13,8 @@ interface TestComponent {
   template: '<button (appDebounceClick)="clickHandler()"></button>'
 })
 class DefaultDebounceTimeTestComponent {
-  @ViewChild(DebounceClickDirective)
-  directive: DebounceClickDirective;
+
+  @ViewChild(DebounceClickDirective) directive!: DebounceClickDirective;
 
   clickHandler: () => void = () => { };
 }
@@ -24,10 +24,9 @@ class DefaultDebounceTimeTestComponent {
   template: '<button (appDebounceClick)="clickHandler()" [appDebounceClickTime]="debounceTime"></button>'
 })
 class CustomDebounceTimeTestComponent {
-  debounceTime: number;
+  debounceTime: number | undefined;
 
-  @ViewChild(DebounceClickDirective)
-  directive: DebounceClickDirective;
+  @ViewChild(DebounceClickDirective) directive!: DebounceClickDirective;
 
   clickHandler: () => void = () => { };
 }
diff --git a/Timeline/ClientApp/src/app/utilities/debounce-click.directive.ts b/Timeline/ClientApp/src/app/utilities/debounce-click.directive.ts
index feb0404e..1d01b671 100644
--- a/Timeline/ClientApp/src/app/utilities/debounce-click.directive.ts
+++ b/Timeline/ClientApp/src/app/utilities/debounce-click.directive.ts
@@ -7,7 +7,7 @@ import { debounceTime } from 'rxjs/operators';
 })
 export class DebounceClickDirective implements OnInit, OnDestroy {
 
-  private subscription: Subscription;
+  private subscription: Subscription | undefined;
 
   @Output('appDebounceClick') clickEvent = new EventEmitter<any>();
 
@@ -34,6 +34,8 @@ export class DebounceClickDirective implements OnInit, OnDestroy {
   }
 
   ngOnDestroy() {
-    this.subscription.unsubscribe();
+    if (this.subscription) {
+      this.subscription.unsubscribe();
+    }
   }
 }
diff --git a/Timeline/ClientApp/src/app/utilities/language-untilities.ts b/Timeline/ClientApp/src/app/utilities/language-untilities.ts
new file mode 100644
index 00000000..be9df2dc
--- /dev/null
+++ b/Timeline/ClientApp/src/app/utilities/language-untilities.ts
@@ -0,0 +1,12 @@
+export function nullIfUndefined<T>(value: T | undefined): T | null {
+  return value === undefined ? null : value;
+}
+
+export function throwIfNullOrUndefined<T>(value: T | null | undefined,
+  lazyMessage: () => string = () => 'Value mustn\'t be falsy'): T | never {
+  if (value === null || value === undefined) {
+    throw new Error(lazyMessage());
+  } else {
+    return value;
+  }
+}