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
.setImageDirectory( htmlOptions.getImageDirectory( ) );
				htmlContext.setSupportedImageFormats( htmlOptions
						.getSupportedImageFormats( ) );
				htmlContext.SetRenderOption( allOptions );
				appContext.put( EngineConstants.APPCONTEXT_HTML_RENDER_CONTEXT,
						htmlContext );
			}
		}
	}
	protected void initializeContentEmitter( IContentEmitter emitter,
			IReportExecutor executor )
	{
		
		HashMap configs = engine.getConfig( ).getEmitterConfigs( );
		IReportContext reportContext = executionContext.getReportContext( );
		IRenderOption options = executionContext.getRenderOption( );
		EngineEmitterServices services = new EngineEmitterServices(
				reportContext, options, configs );
		
		emitter.initialize( services );
	}
	public int getTaskType( )
	{
		return taskType;
	}
	protected void changeStatusToRunning( )
	{
		runningStatus = STATUS_RUNNING;
	}
	protected void changeStatusToStopped( )