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
{
	/**
	 * logger used to log the error.
	 */
	protected static Logger logger = Logger.getLogger( EngineIRVisitor.class
			.getName( ) );
	/**
	 * current report element created by visitor
	 */
	protected Object currentElement;
	/**
	 * default unit used by this report
	 */
	protected String defaultUnit;
	/**
	 * Factory IR created by this visitor
	 */
	protected Report report;