Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* @param propName
	 *            name of the property
	 * @return the value of the property according to the rules explained above
	 */
	public Object getFactoryProperty( Module module, String propName )
	{
		ElementPropertyDefn prop = getPropertyDefn( propName );
		
		if ( prop == null )
			return null;
		return getFactoryProperty( module, prop );
	}
	/**
	 * Resolves a property element reference. The reference is the value of a
	 * property of type property element reference.
	 * 
	 * @param module
	 *            the module information needed for the check, and records any
	 *            errors
	 * @param prop
	 *            the property whose type is element reference
	 * @return the element reference value is always returned, which contains
	 *         the information of element resolution.
	 */
	public ElementRefValue resolveElementReference( Module module,
			ElementPropertyDefn prop )
	{
		Object value = propValues.get( prop.getName( ) );
		assert value == null || value instanceof ElementRefValue;
		assert prop.getTypeCode( ) == PropertyType.ELEMENT_REF_TYPE;