[SQLiteJDBC] NullPointerException when

[jose antonio lorenzo]

I am getting a NullPointerException when using PrepareStatement. The stack
trace is:
Exception in thread "main" java.lang.NullPointerException
        at org.sqlite.PrepStmt.<init>(PrepStmt.java:37)
        at org.sqlite.Conn.prepareStatement(Conn.java:231)
        at org.sqlite.Conn.prepareStatement(Conn.java:224)
        at org.sqlite.Conn.prepareStatement(Conn.java:213)
        at
net.jalorenzofernandez.quiniela.model.Round.writeToDatabase(Round.java:184)

The line of my code that generates the exception is the following
(Round.java: 184):

PreparedStatement ps = conn.prepareStatement("INSERT INTO matches " +
                    "(localId, awayId, localScore, awayScore, division,
year, round) " +
                    "VALUES(?,?,?,?,?,?,?)");

I've checked that conn (a java.sql.Connection instance) is not null. In
fact, before the error, I write to the database using that very connection
without problem. The connection is configured with setAutoCommit(false).
Around 40 commits are made without failure before the error message appears.
Any idea about what I am doing wrong? Thank you for your answers.