java.sql.Connection createArrayOf() always returns null

I am trying to insert a series of values into a sql query using Java's postgresql jdbc4.

java.sql.Connection specifies a method to convert Object[] into java.sql.Array: conn.createArrayOf(String typeName, Object[] elements)

The only problem is, no matter what I try, it always returns null.

public Array makeQueryBigintArray(Object[] values) throws SQLException {
    Array result = conn.createArrayOf("bigint", values);
    // "result" is null at this point, but shouldn't be
    return result;
}

conn is retrieved through a working javax.sql.DataSource via dataSource.getConnection(). conn works for all our other database uses, but its createArrayOf() method always returns null.

I have tried both upper case "BIGINT" and lower case "bigint" for typeName, as per this question, to no avail.

When I dig through the debugger, I find that conn is a org.apache.commons.dbcp.PoolableConnection wrapping a org.postgresql.jdbc4.Jdbc4Connection.

If the feature wasn't supported by postgres/JDBC4, I would expect calling it to throw a SQLException indicating it's unsupported. No exception is thrown.

Any clue as to why it's returning null?

How can I fix it, or else, how can I pass in an array or List of values to a PreparedStatement?