Bug 202236 When select NULL value for multi-value parameter, cause NPE.
Description: When select NULL value for multi-value parameter, cause NPE. Build number: 2.2.1 Steps to reproduce: 1, New a list parameter, check Allow multi-value, uncheck isRequired 2, Select parameter data type as Date 3, Add some items into list 4, Preview 5, Select Null Value item in list Expected result: Can accept Null value for multi-value parameter Actual result: Cause NPE.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineTask.java
{
			log.log( Level.SEVERE,
					MessageConstants.FORMAT_NOT_SUPPORTED_EXCEPTION, format );
			throw new UnsupportedFormatException(
					MessageConstants.FORMAT_NOT_SUPPORTED_EXCEPTION, format );
		}
		pagination = extManager.getPagination( format );
		Boolean outputDisplayNone = extManager.getOutputDisplayNone( format );
		if ( !renderOptions.hasOption( IRenderOption.OUTPUT_DISPLAY_NONE ) )
		{
			renderOptions.setOption( IRenderOption.OUTPUT_DISPLAY_NONE,
					outputDisplayNone );
		}
		IContentEmitter emitter = null;
		try
		{
			emitter = extManager.createEmitter( format, emitterID );
		}
		catch ( Throwable t )
		{
			log.log( Level.SEVERE, "Report engine can not create {0} emitter.", 
					format ); 
			throw new EngineException(
					MessageConstants.CANNOT_CREATE_EMITTER_EXCEPTION, format, t );
		}
		if ( emitter == null )
		{
			log.log( Level.SEVERE, "Report engine can not create {0} emitter.", 
					format ); 
			throw new EngineException(