Bug 142137 Style name can't be changed to None in Property Editor after delete the style
Steps to reproduce: 1.New a style named "S1", apply it on a label 2.Delete "S1" 3.Switch to Property Editor, change label style to None Expected result: Style is changed to None Actual result: Style is still "S1" till change it with context menu
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/StyleCommand.java
/**
	 * Constructor.
	 * 
	 * @param module
	 *            the root of <code>obj</code>
	 * @param obj
	 *            the element to modify.
	 */
	public StyleCommand( Module module, DesignElement obj )
	{
		super( module, obj );
	}
	/**
	 * Sets the style of an element.
	 * 
	 * @param name
	 *            the name of the style to set.
	 * @throws StyleException
	 *             if the element can not have style or the style is not found.
	 */
	public void setStyle( String name ) throws StyleException
	{
		name = StringUtil.trimString( name );
		
		if ( !element.getDefn( ).hasStyle( ) )
			throw new StyleException( element, name,
					StyleException.DESIGN_EXCEPTION_FORBIDDEN );
		StyledElement obj = (StyledElement) element;
		
		ElementPropertyDefn propDefn = obj