> stmt.execute();
>
> // stmt.execute(sqlstring);
>
> ResultSet rs = stmt.executeQuery("SELECT * FROM FEATURES");

Hmmm... Usually such queries are executed with java.sql.Statement, not
with java.sql.PrepapredStatement. So, you have to use either

Statement query = con.createStatement();
ResultSet rs = query.executeQuery("...");
...

or

stmt.close();
stmt = con.prepareStatement("SELECT * FROM FEATURES");
ResultSet rs = stmt.executeQuery();

This should fix the problem.

Anyway, we do have a bug in our code, since NullPointerException
should not happen. I will check this issue, but it will not appear
till next release.

Best regards,
Roman Rokytskyy