fix: Binary handling of empty arrays.

The type of the empty array was not properly read as a result
getting the type of the array caused an NPE
fixes Issue #421 reported by Juha Komulainen

org/postgresql/jdbc2/AbstractJdbc2Array.java

@@ -264,15 +264,30 @@ private ResultSet readBinaryResultSet(int index, int count) throws SQLException
        }
        List rows = new ArrayList();
        Field[] fields = new Field[2];
        if (dimensions > 0) {
            storeValues(rows, fields, elementOid, dims, pos, 0, index);
        }

        storeValues(rows, fields, elementOid, dims, pos, 0, index);

        BaseStatement stat = (BaseStatement) connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
        return stat.createDriverResultSet(fields, rows);
    }

    private int storeValues(List rows, Field[] fields, int elementOid, final int[] dims, int pos, final int thisDimension, int index) throws SQLException {
        if (thisDimension == dims.length - 1) {
    private int storeValues(List rows, Field[] fields, int elementOid, final int[] dims, int pos, final int thisDimension, int index) throws SQLException
    {
        // handle an empty array
        if (dims.length == 0)
        {
            fields[0] = new Field("INDEX", Oid.INT4);
            fields[0].setFormat(Field.BINARY_FORMAT);
            fields[1] = new Field("VALUE", elementOid);
            fields[1].setFormat(Field.BINARY_FORMAT);
            for (int i = 1; i < index; ++i) {
                int len = ByteConverter.int4(fieldBytes, pos); pos += 4;
                if (len != -1) {
                    pos += len;
                }
            }
        }
        else if (thisDimension == dims.length - 1) {
            fields[0] = new Field("INDEX", Oid.INT4);
            fields[0].setFormat(Field.BINARY_FORMAT);
            fields[1] = new Field("VALUE", elementOid);

org/postgresql/test/jdbc2/ArrayTest.java

@@ -413,6 +413,33 @@ public void testNonStandardDelimiter() throws SQLException

        assertTrue(!arrRS.next());
    }

    public void testEmptyBinaryArray() throws SQLException
    {
        
        PreparedStatement pstmt = conn.prepareStatement("SELECT '{}'::int[]");
        // force binary
        ((org.postgresql.PGStatement)pstmt).setPrepareThreshold(-1);
        
        try (ResultSet rs = pstmt.executeQuery()) {
            while (rs.next()) {
                Array array = rs.getArray(1);
                if (!rs.wasNull())
                {
                    ResultSet ars  = array.getResultSet();
                    try
                    {
                        ars.getMetaData().getColumnType(1); // this throws NPE
                    }
                    catch (NullPointerException ex)
                    {
                        assertTrue("should not get here",true);
                    }
                }


            }
        }
    }
        
}