rootPrototype set to nonexistant prototype -> NullPointer

Hi

when copying a app.properties file from an existing app I got a  
NullPointerException

helma.server 2007-04-05 17:00:23,613 -- INFO -- pleon: Exception in  
execute
java.lang.NullPointerException
         at helma.framework.core.Application.createSession 
(Application.java:957)
         at helma.framework.core.Application.execute(Application.java: 
673)
         at helma.servlet.AbstractServletClient.service 
(AbstractServletClient.java:313)
         at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
         at org.mortbay.jetty.servlet.ServletHolder.handle 
(ServletHolder.java:358)
         at org.mortbay.jetty.servlet.ServletHandler.dispatch 
(ServletHandler.java:657)
         at org.mortbay.jetty.servlet.ServletHandler.handle 
(ServletHandler.java:567)
         at org.mortbay.http.HttpContext.handle(HttpContext.java:1807)
         at org.mortbay.http.HttpContext.handle(HttpContext.java:1757)
         at org.mortbay.http.HttpServer.service(HttpServer.java:879)
         at org.mortbay.http.HttpConnection.service 
(HttpConnection.java:789)
         at org.mortbay.http.HttpConnection.handleNext 
(HttpConnection.java:960)
         at org.mortbay.http.HttpConnection.handle 
(HttpConnection.java:806)
         at org.mortbay.http.SocketListener.handleConnection 
(SocketListener.java:218)
         at org.mortbay.util.ThreadedServer.handle 
(ThreadedServer.java:331)
         at org.mortbay.util.ThreadPool$PoolThread.run 
(ThreadPool.java:520)

after some digging around I found the culprit:

rootPrototype = Site

the new app didn't have a Site-prototype. A more helpful error  
message would have saved some minutes

thanks

stefan