private void SaveBtn_Click(object sender, EventArgs e)
        {
            if (!NameTextBox.Text.Trim().Equals(string.Empty) && !LandComboBox.Text.Trim().Equals(string.Empty))
            {
                int ID_Land = Search_Land_ID(LandComboBox.Text.Trim());
                if (ID_Land != 0 && ID_Land != -1)
                {
                    AddHochschule(ID_Land);
                }
                else if (ID_Land == 0)
                {
                    DialogResult dialogResult = MessageBox.Show("Land doesn't exist! Please click Ok to add a new Land!", "confirmation", MessageBoxButtons.OKCancel);
                    if (dialogResult == DialogResult.OK)
                    {
                        Add_Land add_Land = new Add_Land(LandComboBox.Text);
                        this.Close();
                        add_Land.Show();
                    }
                }

                this.Close();
            }
            else
            {
                MessageBox.Show("Please Fill all the field!");
            }
        }
        private void NationalitaetHinzufügenBtn_Click(object sender, EventArgs e)
        {
            Add_Land add_Land = new Add_Land(NationalitaetCB.Text);

            add_Land.Show();
        }
        private void AddNationalitaetBtn_Click(object sender, EventArgs e)
        {
            Add_Land add_Land = new Add_Land(NationalityTB.Text);

            add_Land.Show();
        }