I get a NullPointerException in the cleanup code of org.apache.catalina.session.JDBCStore 
using Tomcat 4.0.4.
This happens while reloading the context.
After the exception tomcat 
hangs until you reload the context again.

I think it can be solved with the following 
'patch'.

--- org/apache/catalina/session/JDBCStore-old.java  Wed Sep  4 02:13:53 2002
+++ 
org/apache/catalina/session/JDBCStore.java      Wed Sep  4 02:18:12 2002
@@ -759,37 +759,43 @@
             
}

             try {
-                preparedSizeSql.close();
+                if (preparedSizeSql != null)
+                    
preparedSizeSql.close();
             } catch (SQLException e) {
                 ;
             }

             try {
-                
preparedKeysSql.close();
+                if (preparedKeysSql != null)
+                    preparedKeysSql.close();
             } 
catch (SQLException e) {
                 ;
             }

             try {
-                preparedSaveSql.close();
+                if (preparedSaveSql 
!= null)
+                    preparedSaveSql.close();
             } catch (SQLException e) {
                 ;
             }

             try {
-                
preparedClearSql.close();
+                if (preparedClearSql != null)
+                    
preparedClearSql.close();
             } catch (SQLException e) {
                 ;
             }

             try {
-                
preparedRemoveSql.close();
+                if (preparedRemoveSql != null)
+                    
preparedRemoveSql.close();
             } catch (SQLException e) {
                 ;
             }

             try {
-                
preparedLoadSql.close();
+                if (preparedLoadSql != null)
+                    preparedLoadSql.close();
             } 
catch (SQLException e) {
                 ;
             }