Fetching a list of Objects and then checking it against a method then returning a new list

Question

sM is an instance of the class, When running the method staffCanWork it is supposed to return a List of staff objects that can work on the given date and time, however when running the method it null pointer errors.

Testing the method within static void main;

 Date date = Date.valueOf(LocalDate.now());
        List<Staff> staff = sM.staffCanWork(date, Time.valueOf(LocalTime.now()));
        for(int i = 0; i < staff.size(); i++){
            System.out.println(staff.get(i).getId());
        }

Method getStaff() using hibernate populates the List with staff objects using hibernate.

    public List<Staff> getStaff(){
        List staff =null;
        Session session = factory.openSession();
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            TypedQuery query = session.getNamedQuery("getStaff");;
            staff = query.getResultList();
        }catch (HibernateException e){
            e.printStackTrace();
        }return staff;
    }

staffCanWork method, Checks through the list to see if staff can work the given date and time.

    public List<Staff> staffCanWork(Date date, Time time){
        List<Staff> staff = getStaff();
        List<Staff> staff1 = null;
        for(int i = 0; i < staff.size(); i++){
            if(staff.get(i).getDoctor() == null){
                if(staff.get(i).getNurse().canWork(date, time)) staff1.add(staff.get(i));
            }
            else {
                if(staff.get(i).getDoctor().canWork(date, time)) staff1.add(staff.get(i));
            }
        }
        System.out.println(staff1.get(0).getId() + "test");
        return staff1;
    }

Method CanWork

public boolean canWork(Date date, Time time){
        Boolean canWork =false;
        Boolean aM = false;

        if(time.getTime() < 12){ aM = true;}
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("E");
        simpleDateFormat.format(date);
        if(aM = true) {
            switch (simpleDateFormat.format(date)) {
                case "Mon": if (getMondayAM() == true) canWork = true;
                    break;
                case "Tue" :if (getTuesdayAM() == true) canWork = true;
                    break;
                case "Wed" :if (getWednesdayAM() == true) canWork = true;
                    break;
                case "Thu" :if (getThursdayAM() == true) canWork = true;
                    break;
                case "Fri" :if (getFridayAM() == true) canWork = true;
                    break;
                case "Sat" :if (getSaturdayAM() == true) canWork = true;
                    break;
                case "Sun" :if (getSundayAM() == true) canWork = true;
                default: return false;
            }
        }
        switch (simpleDateFormat.format(date)) {
            case "Mon": if (getMondayPM() == true) canWork = true;
                break;
            case "Tue" :if (getTuesdayPM() == true) canWork = true;
                break;
            case "Wed" :if (getWednesdayPM() == true) canWork = true;
                break;
            case "Thu" :if (getThursdayPM() == true) canWork = true;
                break;
            case "Fri" :if (getFridayPM() == true) canWork = true;
                break;
            case "Sat" :if (getSaturdayPM() == true) canWork = true;
                break;
            case "Sun" :if (getSundayPM() == true) canWork = true;
            default: return false;
        }
        return canWork;
    }