How to solve this problem?

import java.util.Scanner;

public class Main {
    @SuppressWarnings("InfiniteLoopStatement")
    public static void main(String[] args) {
        while (true) {
            System.out.println("Please choose action from menu:\n" +
                    "1. Register Teacher:\n" +
                    "2. Delete Teacher:\n" +
                    "3. Find Teacher:\n" +
                    "4. Show all Teacher:\n" +
                    "5. Add your classrom to student:\n" +
                    "6. Delete from your classrom students:\n" +
                    "7. Find the Student in your classroom\n" +
                    "8. Show my student in my classroom:\n" +
                    "9. Exit menu:\n");
            int menuId = new Scanner(System.in).nextInt();
            if (menuId == 1) {
                System.out.println("How many teacher will registered? ");
                int countTeacher = new Scanner(System.in).nextInt();//2
                Teacherstore.teachers = new Teacher[countTeacher];
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    System.out.println("Write info detail person: " + (i + 1));

                    System.out.println("Enter id:");
                    int id = new Scanner(System.in).nextInt();

                    System.out.println("Enter name:");
                    String name = new Scanner(System.in).nextLine();

                    System.out.println("Enter surname:");
                    String surname = new Scanner(System.in).nextLine();

                    System.out.println("Enter age:");
                    int age = new Scanner(System.in).nextInt();

                    System.out.println("Enter salary:");
                    double salary = new Scanner(System.in).nextDouble();
                    Teacher teacher = new Teacher(id, name, surname, age, salary);
                    Teacherstore.teachers[Teacherstore.currentTeacher++] = teacher;
                    System.out.println("Teacher succesfully registred: " + teacher);
                    System.out.println();
                }
            } else if (menuId == 2) {
                System.out.println("Write id to delete following Teacher: ");
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    if (Teacherstore.teachers[i] != null) {
                        System.out.println(Teacherstore.teachers[i]);
                    }
                }
                int teacherDelete = new Scanner(System.in).nextInt();
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    if (Teacherstore.teachers[i] != null && Teacherstore.teachers[i].getId() == teacherDelete) {
                        System.out.println("Teacher successfully deleted: " + Teacherstore.teachers[i]);
                        Teacherstore.teachers[i] = null;
                    }
                }
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    if (Teacherstore.teachers[i] != null) {
                        System.out.println("Teachers remaining in the database: " + Teacherstore.teachers[i]);
                    }
                }

            } else if (menuId == 3) {
                System.out.println("Write id,name,surname or salary to find Teacher: ");
                String findKey = new Scanner(System.in).nextLine();
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    if (Teacherstore.teachers[i] != null) {
                        if (Teacherstore.teachers[i].getId().toString().contains(findKey) ||
                                Teacherstore.teachers[i].getName().contains(findKey) ||
                                Teacherstore.teachers[i].getSurname().contains(findKey) ||
                                Teacherstore.teachers[i].getAge().toString().contains(findKey) ||
                                Teacherstore.teachers[i].getSalary().toString().contains(findKey)) {
                            System.out.println("Founded teacher:" + Teacherstore.teachers[i]);
                        }
                    }
                }
            } else if (menuId == 4) {
                System.out.println("Teachers remaining in the database: ");
                for (int i = 0; i < Teacherstore.teachers.length; i++) {
                    if (Teacherstore.teachers[i] != null) {
                        System.out.println(Teacherstore.teachers[i]);
                    }
                }
                System.out.println();
            } else if (menuId == 5) {
                System.out.println("How many student add your classroom: ");
                int countStudents = new Scanner(System.in).nextInt();
                Teacher.studentsTeacher = new Student[countStudents];
                for (int i = 0; i < Teacher.studentsTeacher.length; i++) {
                    System.out.println("Write info detail student: " + (i + 1));

                    System.out.println("Enter id: ");
                    int id = new Scanner(System.in).nextInt();

                    System.out.println("Enter name: ");
                    String name = new Scanner(System.in).nextLine();

                    System.out.println("Enter surname: ");
                    String surname = new Scanner(System.in).nextLine();

                    System.out.println("Enter age: ");
                    int age = new Scanner(System.in).nextInt();

                    System.out.println("Enter scholarship: ");
                    double scholarship = new Scanner(System.in).nextDouble();
                    Student student = new Student(id, name, surname, age, scholarship);
                    Teacher.studentsTeacher[i] = student;
                    System.out.println("Student succesfully add the classrom: " + student);
                    System.out.println();
                }

            } else if (menuId == 6) {
                System.out.println("Which student do you want to delete from your class?");
                for (int i = 0; i < Teacher.studentsTeacher.length; i++) {
                    if (Teacher.studentsTeacher[i] != null) {
                        System.out.println(Teacher.studentsTeacher[i]);
                        break;
                    }
                }
                String deleteStudent = new Scanner(System.in).nextLine();
                for (int i = 0; i < Teacher.studentsTeacher.length; i++) {
                    if (Teacher.studentsTeacher[i] != null && Teacher.studentsTeacher[i].getId().toString().contains(deleteStudent)) {
                        System.out.println("Student successfully deleted from your classrom: " + Teacher.studentsTeacher[i]);
                        Teacher.studentsTeacher = null;
                        break;
                    } else if (Teacher.studentsTeacher[i] != null && Teacher.studentsTeacher[i].getName().contains(deleteStudent)) {
                        System.out.println("Student successfully deleted from your classrom: " + Teacher.studentsTeacher[i]);
                        Teacher.studentsTeacher = null;
                        break;
                    } else if (Teacher.studentsTeacher[i] != null && Teacher.studentsTeacher[i].getSurname().contains(deleteStudent)) {
                        System.out.println("Student successfully deleted from your classrom: " + Teacher.studentsTeacher[i]);
                        Teacher.studentsTeacher = null;
                        break;
                    } else if (Teacher.studentsTeacher[i] != null && Teacher.studentsTeacher[i].getAge().toString().contains(deleteStudent)) {
                        System.out.println("Student successfully deleted from your classrom: " + Teacher.studentsTeacher[i]);
                        Teacher.studentsTeacher = null;
                        break;
                    } else if (Teacher.studentsTeacher[i] != null && Teacher.studentsTeacher[i].getScholarship().toString().contains(deleteStudent)) {
                        System.out.println("Student successfully deleted from your classrom: " + Teacher.studentsTeacher[i]);
                        Teacher.studentsTeacher = null;
                        break;
                    }
                }
            } else if (menuId == 8) {
                System.out.println("Students in your classrom: ");
                for (int i = 0; i < Teacher.studentsTeacher.length; i++) {
                    if (Teacher.studentsTeacher[i] != null) {
                        System.out.println(Teacher.studentsTeacher[i]);
                    }
                }
                System.out.println();
            }

        }
    }
}

What I have tried:

I tried solve the NullPointerException.