Fix broken cart cleanup

This fixes an error occuring when multiple employees were
added to the event before checkout.

src/main/java/catering/order/CustomCart.java

@@ -11,7 +11,7 @@ import java.util.HashSet;
 import java.util.Set;
 
 public class CustomCart extends Cart {
-	private final Set<Employee> staff;
+	private Set<Employee> staff;
 	private OrderType orderType;
 	private LocalDateTime start;
 	private LocalDateTime finish;
@@ -31,12 +31,12 @@ public class CustomCart extends Cart {
 	 * Adds an employee to the cart
 	 */
 	public boolean addEmployee(Employee employee) {
-		for (Employee myEmployee : this.staff) {
+		for (Employee myEmployee : staff) {
 			if (myEmployee.equals(employee)) {
 				return false;
 			}
 		}
-		return this.staff.add(employee);
+		return staff.add(employee);
 	}
 
 	public Set<Employee> getStaff() {
@@ -44,9 +44,9 @@ public class CustomCart extends Cart {
 	}
 
 	public boolean removeEmployee(Employee employee) {
-		for (Employee myEmployee : this.staff) {
+		for (Employee myEmployee : staff) {
 			if (myEmployee.equals(employee)) {
-				return this.staff.remove(myEmployee);
+				return staff.remove(myEmployee);
 			}
 		}
 		return false;
@@ -56,7 +56,7 @@ public class CustomCart extends Cart {
 	 * Add staff to order (analogous to cart.addItemsTo(order))
 	 */
 	public CustomOrder addStaffTo(CustomOrder order) {
-		for (Employee employee : this.staff) {
+		for (Employee employee : staff) {
 			order.addEmployee(employee);
 		}
 
@@ -106,12 +106,16 @@ public class CustomCart extends Cart {
 			total = total.add(Money.of(getDurationInHoursTimesRate(12.0), "EUR"));
 		}
 
+		for (Employee employee : staff) {
+			total = total.add(Money.of(getDurationInHoursTimesRate(12), "EUR")); // TODO: get from employee
+		}
+
 		return total;
 	}
 
 	@Override
 	public void clear() {
 		super.clear();
-		staff.forEach(staff::remove);
+		staff = new HashSet<>();
 	}
 }