NPE in request.getRequestURL()

[Jerry Malcolm]

Can anyone tell me what I might be doing that would cause an NPE inside 
the request object on getRequestURL()?  The NPE only happens about 10% 
of the time.  I can't figure out what is happening differently in that 
10% of the calls to this code.  Thx

java.lang.NullPointerException
        at 
org.apache.catalina.connector.Request.getRequestURL(Request.java:2465)
        at 
org.apache.catalina.connector.RequestFacade.getRequestURL(RequestFacade.java:868)