timestamp parameter is null

Hello List!

I have the following problem:

I'm trying to execute a simple SQL query with JDBC and I get an
exception, which I don't understand why. Here's the code:

    public static void main(String[] args) throws Exception {
        Class.forName("org.postgresql.Driver");
        Connection conn =
DriverManager.getConnection("jdbc:postgresql://localhost:5434/dbname",
"user", "pass");
        PreparedStatement stm = conn.prepareStatement("select * from
tablename where ? is not null");
        stm.setTimestamp(1, new Timestamp(new Date().getTime()));
        stm.executeQuery();
    }

The exception is:

Exception in thread "main" org.postgresql.util.PSQLException: ERROR:
could not determine data type of parameter $1
    at
org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:1512)
    at
org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1297)
    at
org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:188)
    at
org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:430)
    at
org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:346)
    at
org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:250)
    at Test6.main(Test6.java:15)

The server version is 8.1.0. The Jdbc driver is
postgresql-8.1-404.jdbc3.jar.

The same code runs fine with the 7.4 jdbc driver. It's also okay, if I'm
using any other type than timestamp. Actually, I tried "string" and it
worked.

I wonder what the problem is.

Marci