java.lang.NullPointerException java

import java.awt.Graphics;


public class Cegielka {
	private int x, y;
	private int w, h;
	private boolean s;
	
	public Cegielka()
	{
		s = true;
	}
	
	public int getX()
	{
		return x;
	}
	
	public int getY()
	{
		return y;
	}
	 public int getW()
	 {
		 return w;
	 }
	 
	 public int getH()
	 {
		 return h;
	 }
	 
	 public boolean getS()
	 {
		 return s;
	 }
	 
	 public void setX(int nX)
	 {
		 x = nX;
	 }
	 
	 public void setY(int nY)
	 {
		 y = nY;
	 }
	 
	 public void setW(int nW)
	 {
		 w = nW;
	 }
	 
	 public void setH(int nH)
	 {
		 h = nH;
	 }
	 
	 public void setS(boolean bS)
	 {
		 s = bS;
	 }
	 
	 public void wyswietlCegielke(Graphics g)
	 {
		 g.fillRect(x, y, w, h);
	 }
}

public Cegielka [][] zbudujCegielki(int xE, int yE)
		{
			Cegielka [][] c = new Cegielka [10][20];
			double ax = 0.005 * xE;
			double ay = 0.04 * yE;
			
			for (int i = 0; i < 10; i++)
			{
				for (int j = 0; j < 20; j++)
				{
					c[i][j].setX((int)(ax));
					c[i][j].setY((int)(ay));
					c[i][j].setW((int)(0.04 * xE));
					c[i][j].setH((int)(0.02 * yE));
					
					ax += 0.05 * xE;
				}
				
				ay += 0.03 * yE;
				ax = 0.005 * xE;
			}
			
			return c;
		}

c[i][j] = new Cegielka(); 

 
for (int i = 0; i < 10; i++)
{
             for (int j = 0; j < 20; j++)
             {
                  c[i][j] = new Cegielka(); 
                  ......
              }
}