Fixed some Parser bugs where empty inputs cause a runtime error.

Author: Hardoh

.gitignore

@@ -13,3 +13,4 @@ src/main/resources/docs/
 *.iml
 bin/
 data
+MANIFEST.MF

src/main/java/duke/command/AddCommand.java

@@ -16,7 +16,8 @@ public AddCommand(String toAdd, Task.TaskType taskType) {
 
     public void execute(TaskList taskList, Storage storage) {
         Task newTask = taskList.AddTask(toAdd, taskType);
-        storage.SaveTaskToFile(newTask);
+        if (newTask != null)
+            storage.SaveTaskToFile(newTask);
     }
 
     public boolean isExit() {

src/main/java/duke/interaction/Parser.java

@@ -17,15 +17,15 @@ public static Command parse(String fullCommand) {
                 case "bye":
                     return new ExitCommand();
                 case "done":
-                    return new DoneCommand(in.nextInt() - 1);
+                    return new DoneCommand((in.hasNextInt() ? in.nextInt() - 1 : -1));
                 case "todo":
-                    return new AddCommand(in.nextLine().trim(), Task.TaskType.TODO);
+                    return new AddCommand((in.hasNextLine() ? in.nextLine().trim() : ""), Task.TaskType.TODO);
                 case "deadline":
-                    return new AddCommand(in.nextLine(), Task.TaskType.DEADLINE);
+                    return new AddCommand((in.hasNextLine() ? in.nextLine().trim() : ""), Task.TaskType.DEADLINE);
                 case "event":
-                    return new AddCommand(in.nextLine(), Task.TaskType.EVENT);
+                    return new AddCommand((in.hasNextLine() ? in.nextLine().trim() : ""), Task.TaskType.EVENT);
                 case "delete":
-                    return new DeleteCommand(in.nextInt() - 1);
+                    return new DeleteCommand((in.hasNextInt() ? in.nextInt() - 1 : -1));
                 case "date":
                     return new DateCommand(in.nextLine().trim());
                 default: