Bug 213680 [2.2.2]Chart script can not be cleaned completely.
Description: Reset script or delete all script does not work. build version: v20071221-0630 steps to reproduce: 1. New a report. 2. New a chart. 3. Enter some script for the chart and save the report. 4. Click the reset scirpt button or delete all script. 5. Save the report and switch to layout,then switch back to script page. Expected result: Script are cleaned. Actual result: Script are not cleaned. Note: If you delete part of the script, it works.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/extension/PeerExtensibilityProvider.java
* @return the extension model properties, null if extended element is null
	 */
	private IPropertyDefinition[] getExtensionModelPropertyDefns( )
	{
		if ( reportItem == null )
			return null;
		return reportItem.getPropertyDefinitions( );
	}
	/**
	 * Gets the list of style masks for Model style properties.
	 * 
	 * @return the list of the style masks
	 */
	protected List getStyleMasks( )
	{
		return Collections.EMPTY_LIST;
	}
	/**
	 * Returns the value of extension property or extension model property.
	 * 
	 * @param propName
	 *            name of the property
	 * @return the value of the given property. If the property is not found, or
	 *         the value is not set, return null.
	 */
	public Object getExtensionProperty( String propName )
	{
		if ( isExtensionXMLProperty( propName ) && hasOwnModel( propName ) )
		{
			if ( reportItem != null )