Bug 121687 Exception throws when export data in table which inside a grid cell.
Description: Exception throws when export data in table which inside a grid cell. Steps to reproduce: 1. insert a grid. 2. insert one table to one grid cell. 3. insert another table to the other grid cell. 4. export data in two tables. Expected result: Data are exported. Actual result: Exception in: ReportEngineService.getMetaData( )
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/parser/EngineIRVisitor.java
{
			VisibilityDesign visibility = new VisibilityDesign( );
			while ( visibilityRulesIterator.hasNext( ) )
			{
				VisibilityRuleDesign hide = createHide( (HideRuleHandle) visibilityRulesIterator
						.next( ) );
				visibility.addRule( hide );
			}
			if ( visibility.count( ) == 0 )
			{
				return null;
			}
			return visibility;
		}
		return null;
	}
	/**
	 * Creates the visibility rule( i.e. the hide)
	 * 
	 * @param handle
	 *            the DE's handle
	 * @return the created visibility rule
	 */
	protected VisibilityRuleDesign createHide( HideRuleHandle handle )
	{
		VisibilityRuleDesign rule = new VisibilityRuleDesign( );
		rule.setExpression( createExpression( handle.getExpression( ) ) );
		rule.setFormat( handle.getFormat( ) );
		return rule;
	}