Bug 124600 delete Grid Column causes NPE thrown out in error log
steps to reproduce: - insert a 3*3 grid - delete grid columns one by one expected behavior: - these operations should completed without any error. actual behavior: - after i deleted the 3rd column, NPE was thrown out in error log.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DNDUtil.java
{
				return ( (GridHandle) parent ).canInsertAndPasteColumn(
						transferData, columnNumber );
			}
			return ( (GridHandle) parent ).canPasteColumn( transferData,
					columnNumber, true );
		}
		return false;
	}
	protected static int handleValidateTargetCanContainByContainer(
			Object targetObj, DesignElementHandle childHandle,
			boolean validateContainer )
	{
		targetObj = unwrapToModel( targetObj );
		if ( targetObj instanceof DesignElementHandle )
		{
			return handleValidateTargetCanContainElementHandle(
					(DesignElementHandle) targetObj, childHandle,
					validateContainer );
		}
		if ( targetObj instanceof SlotHandle )
		{
			SlotHandle targetHandle = (SlotHandle) targetObj;
			return targetHandle.getElementHandle( ).canContain(
					targetHandle.getSlotID( ), childHandle )
					? CONTAIN_THIS
					: CONTAIN_NO;
		}
		return CONTAIN_NO;
	}