diff --git a/src/main/java/org/kryptojagd/controls/AbstractController.java b/src/main/java/org/kryptojagd/controls/AbstractController.java
index 6710ba6..91a969a 100644
--- a/src/main/java/org/kryptojagd/controls/AbstractController.java
+++ b/src/main/java/org/kryptojagd/controls/AbstractController.java
@@ -11,6 +11,11 @@ public abstract class AbstractController {
 	 */
 	static MainController mainController;
 
+	/**
+	 * Updates the timer in the corresponding window.
+	 */
+	void updateTimer(){}
+
 	/**
 	 * Sets main controller.
 	 *
diff --git a/src/main/java/org/kryptojagd/controls/DecryptionController.java b/src/main/java/org/kryptojagd/controls/DecryptionController.java
index 2110efa..636bd85 100644
--- a/src/main/java/org/kryptojagd/controls/DecryptionController.java
+++ b/src/main/java/org/kryptojagd/controls/DecryptionController.java
@@ -115,6 +115,7 @@ private void clickAnswer(Button procedure){
      * Updates the {@link DecryptionController#timer} every second in the corresponding fxml-file.
      */
     @FXML
+    @Override
     void updateTimer() {
         Timeline time = new Timeline();
         time.setCycleCount(Timeline.INDEFINITE);
diff --git a/src/main/java/org/kryptojagd/controls/EncryptionController.java b/src/main/java/org/kryptojagd/controls/EncryptionController.java
index a8cf602..905ada9 100644
--- a/src/main/java/org/kryptojagd/controls/EncryptionController.java
+++ b/src/main/java/org/kryptojagd/controls/EncryptionController.java
@@ -64,6 +64,7 @@ void checkEncryption(ActionEvent event) {
      * Updates the {@link EncryptionController#timer} every second in the corresponding fxml-file.
      */
     @FXML
+    @Override
     void updateTimer() {
         Timeline time = new Timeline();
         time.setCycleCount(Timeline.INDEFINITE);
diff --git a/src/main/java/org/kryptojagd/controls/MultipleChoiceController.java b/src/main/java/org/kryptojagd/controls/MultipleChoiceController.java
index 243842a..1939b59 100644
--- a/src/main/java/org/kryptojagd/controls/MultipleChoiceController.java
+++ b/src/main/java/org/kryptojagd/controls/MultipleChoiceController.java
@@ -117,6 +117,7 @@ private void clickAnswer(String answer){
      * Updates the {@link MultipleChoiceController#timer} every second in the corresponding fxml-file.
      */
     @FXML
+    @Override
     void updateTimer() {
         Timeline time = new Timeline();
         time.setCycleCount(Timeline.INDEFINITE);
diff --git a/src/main/java/org/kryptojagd/controls/TaskFinishedController.java b/src/main/java/org/kryptojagd/controls/TaskFinishedController.java
index 88fb8aa..5a17070 100644
--- a/src/main/java/org/kryptojagd/controls/TaskFinishedController.java
+++ b/src/main/java/org/kryptojagd/controls/TaskFinishedController.java
@@ -107,6 +107,7 @@ void nextWindow(ActionEvent event) {
 	 * Updates the {@link TaskFinishedController#timer} every second in the corresponding fxml-file.
 	 */
 	@FXML
+	@Override
 	void updateTimer() {
 		Timeline time = new Timeline();
 		time.setCycleCount(Timeline.INDEFINITE);
diff --git a/src/main/java/org/kryptojagd/presentation/PresentationManager.java b/src/main/java/org/kryptojagd/presentation/PresentationManager.java
index 168191f..5ebf60b 100644
--- a/src/main/java/org/kryptojagd/presentation/PresentationManager.java
+++ b/src/main/java/org/kryptojagd/presentation/PresentationManager.java
@@ -1,6 +1,8 @@
 package org.kryptojagd.presentation;
 
 import java.io.IOException;
+import java.util.Objects;
+
 import javafx.application.Platform;
 import javafx.fxml.FXMLLoader;
 import javafx.scene.Parent;
@@ -34,7 +36,7 @@ public void switchWindow(String str) {
 		Parent root;
 		try {
 
-			root = FXMLLoader.load(getClass().getResource(str));
+			root = FXMLLoader.load(Objects.requireNonNull(getClass().getResource(str)));
 			// root = loader.load();
 			Scene scene = new Scene(root);	
 			stage.setScene(scene);