See data lines for the set_data() method.
Please note how the first two values and last two values are null and do not show in the graph. There are further null values that are skipped.
<?php
include_once 'ofc-library/open_flash_chart_object.php';
open_flash_chart_object( 400, 250, 'http://'. $_SERVER['SERVER_NAME'] .'/open-flash-chart/gallery-data-30.php' );
?>
<?php
include_once( 'ofc-library/open-flash-chart.php' );
$g = new graph();
$g->set_x_label_style( 10, '#9933CC' );
$g->y_label_steps( 8 );
$g->area_hollow( 2, 3, 25, '#CC3399', 'Price', 12 );
$g->set_y_min( 0 );
$g->set_y_max( 40000 );
$tmp = array();
$tmp[] = '2007-06-22';
$tmp[] = '2007-06-23';
$tmp[] = '2007-06-24';
$tmp[] = '2007-06-25';
$tmp[] = '2007-06-26';
$tmp[] = '2007-06-27';
$tmp[] = '2007-06-28';
$tmp[] = '2007-06-29';
$tmp[] = '2007-06-30';
$tmp[] = '2007-06-31';
$tmp[] = '2007-07-01';
$tmp[] = '2007-07-02';
$tmp[] = '2007-07-03';
$tmp[] = '2007-07-04';
$g->set_x_labels( $tmp );
//
// now set up an array of values to
// show in the chart, this includes
// a number of null values which
// will NOT be plotted.
//
$data = array();
$data[] = 'null';
$data[] = 'null';
$data[] = '33188';
$data[] = '34019';
$data[] = '34692';
$data[] = 'null';
$data[] = 'null';
$data[] = 'null';
$data[] = '36319';
$data[] = 'null';
$data[] = 'null';
$data[] = '37089';
$data[] = 'null';
$data[] = 'null';
$g->set_data( $data );
$g->bg_colour = '#E0E0E0';
$g->set_inner_background( '#DDEFFA', '#CBD7E6', 90 );
$g->x_axis_colour( '#799191', '#FFFFFF' );
$g->y_axis_colour( '#799191', '#FFFFFF' );
$g->set_x_label_style( 10, '#CC3399', 2 );
$g->set_y_label_style( 10, '#CC3399' );
$g->title( 'Avg. Property Value (showing null values)', '{font-size: 14px; color: #CC3399}' );
$g->set_tool_tip( 'USD $#val#' );
echo $g->render();
?>