Problema ao selecionar item dentro do JComboBox

JComboBox cb = new JComboBox();

//Pegar uma lista de objetos (aqui Cliente, esse objeto deve estar com o metodos: equals, compareTo e hashCode)
ArrayList<Cliente> lista = new ClienteDAO().lista();

// Criar o modelo que vai usar no componente
ArrayListComboBoxModel modeloLista = new ArrayListComboBoxModel(lista);

// Associar o modelo ao JComboBox
cb.setModel(modeloLista);

// Criar um item qualquer o qual queira selecionar no modelo (e JComboBox)
Cliente item = new Cliente();
item.setNome("Nome do cliente");
item.setCodigo(123);

// Selecionar diretametne no modelo
modeloLista.setSelectedItem(item);

import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractListModel;
import javax.swing.MutableComboBoxModel;

public class ArrayListComboBoxModel extends AbstractListModel implements MutableComboBoxModel {

    private Object selectedItem;
    private List list;

    public ArrayListComboBoxModel() {
        this.list = new ArrayList();
    }

    public ArrayListComboBoxModel(List list) {
        this.list = new ArrayList(list);
    }

    public void setList(List list) {
        this.list = list;
        fireContentsChanged(this, 0, list.size());
    }

    @Override
    public int getSize() {
        return list.size();
    }

    @Override
    public Object getElementAt(int i) {
        try {
            return list.get(i);
        } catch (java.lang.IndexOutOfBoundsException ex) {
            return null;
        }
    }

    @Override
    public Object getSelectedItem() {
        return selectedItem;
    }

    public Integer getSelectedIndex() {
        int index = list.indexOf(this.getSelectedItem());
        return index;
    }

    @Override
    public void setSelectedItem(Object newValue) {
        selectedItem = newValue;
        fireContentsChanged(this, -1, list.size());
    }

    // MutableComboBoxModel
    public void setElementAt(Object element, int index) {
        list.set(index, element);
        // Added at end, notify ListDataListener objects
        int length = getSize();
        fireIntervalAdded(this, length - 1, length - 1);
    }

    // MutableComboBoxModel
    @Override
    public void addElement(Object element) {
        list.add(element);
        // Added at end, notify ListDataListener objects
        int length = getSize();
        fireIntervalAdded(this, length - 1, length - 1);
    }

    @Override
    public void insertElementAt(Object element, int index) {
        // Insert the element at the specified position
        list.add(index, element);
        // Added in middle, notify ListDataListener objects
        fireIntervalAdded(this, index, index);
    }

    @Override
    public void removeElement(Object element) {
        // Find out position
        int index = list.indexOf(element);
        if (index != -1) {
            // Remove an element
            list.remove(element);
            // Removed from middle, notify ListDataListener objects
            fireIntervalRemoved(this, index, index);
        }
    }

    public void removeAllItens() {
        if (list != null && list.size() > 0) {
            list.clear();
            fireContentsChanged(this, -1, list.size());
        }
    }

    @Override
    public void removeElementAt(int index) {
        if (getSize() >= index) {
            // Remove an element at the specified position
            list.remove(index);
            // Removed from index, notify ListDataListener objects
            fireIntervalRemoved(this, index, index);
        }
    }
}

private void listaCombo() throws SQLException{
        CadastroDao dao = new CadastroDao();
        ArrayList<Cadastro> minhalista = (ArrayList<Cadastro>) dao.getListaCombo();
        
        DefaultComboBoxModel defaultComboBox = new
                DefaultComboBoxModel(minhalista.toArray());

        CbxCadastro.setMaximumRowCount(5);
        CbxCadastro.setModel(defaultComboBox);
        CbxCadastro.setSelectedIndex(-1);

        EdtNome.setText(CbxCadastro.getSelectedItem().toString());
        EdtCodigo.setText(String.valueOf(CbxCadastro.getSelectedIndex()));
 }

CbxCadastro.setSelectedIndex(-1);

java.lang.NullPointerException