Merge branch 'master' into branch-A-CodeQuality

src/main/java/duke/storage/Storage.java

@@ -7,6 +7,7 @@
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 
 import duke.exceptions.DukeException;
 import duke.exceptions.DukeIoException;
@@ -83,6 +84,7 @@ public void load(TaskList tasklist) throws DukeException {
      * @throws DukeException If there is an error saving tasks to the save file.
      */
     public void save(TaskList tasklist) throws DukeException {
+        assert Files.exists(Paths.get(this.path)) : "Save file should exist before saving tasks to file.";
         try {
             String content = "";
             FileWriter fileWriter = new FileWriter(path, false);

src/main/java/duke/tasks/Task.java

@@ -32,6 +32,7 @@ public abstract class Task {
      * @param input The description of the task.
      */
     public Task(String input) {
+        assert input != null && input != "" : "Description of a task should not be empty.";
         this.description = input;
         this.isDone = false;
     }