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
{
		ElementDefn defn = (ElementDefn) getDefn( );
		SlotDefn slotDefn = (SlotDefn) defn.getSlot( slotID );
		if ( slotDefn == null )
		{
			return null;
		}
		String slotSelector = slotDefn.getSelector( );
		if ( StringUtil.isBlank( slotSelector ) )
		{
			return null;
		}
		return slotSelector;
	}
	/**
	 * Returns the property value.
	 * 
	 * @param module
	 *            the module
	 * @param prop
	 *            the definition of property
	 * @return the property value, or null if no value is set.
	 */
	public Object getProperty( Module module, PropertyDefn prop )
	{
		return getProperty( module, (ElementPropertyDefn) prop );
	}
	/**
	 * Returns whether this element is a style. While this information could be
	 * computed from meta-data, it is computed here for performance.