JTable con JCheckBox y celdas NULL

+----------+--------+--------+
|texto0 |check  |check  |
|texto1 |(vacio)|check  |
|texto2 |check  |(vacio)|
|texto3 |check  |check  |
+----------+--------+--------+

package org.bolivia.app;
import javax.swing.table.AbstractTableModel;
/**
 * @web https://www.jc-mouse.net/
 * @author Mouse
 */
public class MyTableModel extends AbstractTableModel{

    private String[] columnNames;
    private Object[][] data;

    /** Constructor de clase */
    public MyTableModel( String[] columnNames, Object[][] data )
    {
        this.columnNames = columnNames;
        this.data = data;
    }  

    @Override
    public int getRowCount() {
        return data.length;
    }

    @Override
    public int getColumnCount() {
        return columnNames.length;
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        return data[rowIndex][columnIndex];
    }

    @Override
    public void setValueAt(Object value, int row, int column) {      
        data[row][column] = value;
    }

    @Override
    public String getColumnName(int column) {
        return columnNames[column];
    }

    @Override
    public Class getColumnClass(int column) {
        return getValueAt(0, column).getClass();
    }

     @Override
    public boolean isCellEditable(int row, int column) {      
      if( data[row][column]==null )                
          return false;
      return true;
    }

}

package org.bolivia.app;
import java.awt.Color;
import java.awt.Component;
import javax.swing.JCheckBox;
import javax.swing.JLabel;
import javax.swing.JTable;
import javax.swing.table.DefaultTableCellRenderer;
/**
 * @web https://www.jc-mouse.net/
 * @author Mouse
 */
public class CellRenderer extends DefaultTableCellRenderer  {

    private JCheckBox check = new JCheckBox();  

    /** Constructor de clase*/
    public CellRenderer(){}        

     @Override
    public Component getTableCellRendererComponent ( JTable table, Object value, boolean selected, boolean focused, int row, int column )
    {
        //color de celda seleccionada
        this.setBackground( (selected)? new Color( 50, 153 , 254):new Color(255,255,255) );             
        //
        if( column == 1 || column == 2 || column == 3 )
        {
            Boolean bol = Boolean.valueOf(String.valueOf(value));
            if( value == null  )
            {             
                return null;
            }
            else // es un boolean
            {   
                check = new JCheckBox();                                
                check.setHorizontalAlignment( JLabel.CENTER );                
                check.setBackground( (selected)? new Color( 50, 153 , 254):new Color(255,255,255) );
                check.setSelected( bol ); //valor de celda 
                return check;
            }                     
        }

        return this;
    }    

}//--> fin clase

Object[][] data = { {"César Noso",true,false,true},
                        {"Ana Busado de Hesa",false,null,true},
                        {"Lucila Tanga",true,null,null},
                        {"Ester Mosobicho ",null,true,null},
                        {"Mikoko Yanosuda",true,null,true},
                        {"Keko Jones",true,false,null},
                        {"Ana Mier de Cilla",true,false,true},
                        {"Ana Pulpito Salido",null,false,false},
                        {"Jack Hallate",true,false,false},
                        {"Evaristo Piernabierta Zas",false,null,false},
                        {"Pascual Conejo Enamorado",true,false,null}