Java Database Connectivity (JDBC)

All

I am able to successfully establish a connection to a DB2 database, but when I try to close the connection I get a NullPointerException. This is just a simple test program using the following code:

public Conn()
{
String query = "SELECT CUSNBR FROM ECLIB.CUSUSRMP";

System.out.println("Making new Conn object...");
try
{
System.out.println("Calling getDbConnection() method...");
if (conn == null)
{
Class.forName("com.ibm.as400.access.AS400JDBCDriver");
System.out.print("Connecting...");
conn = DriverManager.getConnection("jdbc:as400://ATIESRV1;prefetch=true;prompt=false", USER, PASSWORD);
conn.setAutoCommit(false);
System.out.println("Connected to AS/400.");

Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(query);

while(rs.next())
{
String name = rs.getInt("CUSNBR");
System.out.println("Name: " + name);
}

System.out.println("Attempting to close the connection...");
// closing connections/Objects
if (conn != null)
{
System.out.println("conn is NOT null");
rs.close();
st.close();
conn.close();
}
System.out.println("Connection successfully closed !!!");
}
}
catch(AS400JDBCException e)
{
System.out.println("AS400JDBCException occurred: " + e.getMessage());
e.printStackTrace();
}
catch(SQLException e)
{
System.out.println("SQLException occurred: " + e.getMessage());
e.printStackTrace();
}
catch(NullPointerException e)
{
System.out.println("NullPointerException occurred: " + e.getMessage());
}
catch(Exception e)
{
System.out.println("General Exception occurred: " + e.getMessage());
}
}

I don't see the problem. Why is this happening ???
Thanks ...