JDBC driver problems with tomcat

Hello to everybody,
I am running postgresquel 6.5.3 and tomcat 4.0.
Everything works fine when I access databases from servlets or JSP but I
can't authenticate users with JDBCRealms in tomcat using postgresql
databases.
If I try to start Tomcat I get this error from the JDBC driver. I am
using the driver jdbc6.5-1.2.jar

java.lang.NullPointerException:
at java.util.StringTokenizer.<init>(StringTokenizer.java:93)
at postgresql.Driver.parseURL(Driver.java:240)
at postgresql.Driver.connect(Driver.java:109)
at org.apache.catalina.realm.JDBCRealm.open(JDBCRealm.java:548)
at org.apache.catalina.realm.JDBCRealm.start(JDBCRealm.java:613)
at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1108)
at
org.apache.catalina.core.StandardContext.start(StandardContext.java:3334)
at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1123)
at
org.apache.catalina.core.StandardHost.start(StandardHost.java:612)
at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1123)
at
org.apache.catalina.core.StandardEngine.start(StandardEngine.java:307)
at
org.apache.catalina.core.StandardService.start(StandardService.java:388)
at
org.apache.catalina.core.StandardServer.start(StandardServer.java:505)
at org.apache.catalina.startup.Catalina.start(Catalina.java:776)
at org.apache.catalina.startup.Catalina.execute(Catalina.java:681)
at org.apache.catalina.startup.Catalina.process(Catalina.java:179)
at java.lang.reflect.Method.invoke(Native Method)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:243)

Is there a way to use Postgresql in JDBRealms?
Thanks in advance
Francesco Lunelli