Calling Servlet from another servlet error using orion

[rosely kumoi]

I got a null pointer exception when I try to get another servlet
reference from other servlet
using this command:

BookDBServlet database = (BookDBServlet)
getServletConfig().getServletContext().getServlet("bookstore.BookDBServlet");

BookDetails bd = database.getBookDetails(bookId); //null pointer
exception here

here are the stacktrace:

500 Internal Server Error

java.lang.NullPointerException:
        at bookstore.BookDetailServlet.doGet(BookDetailServlet.java:57)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java)
        at com.evermind.server.http.df.o3(JAX)
        at com.evermind.server.http.df.forward(JAX)
        at com.evermind.server.http.dm.o9(JAX, Compiled Code)
        at com.evermind.server.http.dm.o8(JAX, Compiled Code)
        at com.evermind.util.e.run(JAX, Compiled Code)