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
ScriptedDesignVisitor visitor = new ScriptedDesignVisitor(
				reportDesign, executionContext );
		visitor.apply( reportDesign.getRoot( ) );
		runnable.setDesignHandle( reportDesign );
	}
	protected void startFactory( )
	{
		ReportDesignHandle reportDesign = executionContext.getDesign( );
		ReportScriptExecutor.handleBeforeFactory( reportDesign,
				executionContext );
	}
	protected void closeFactory( )
	{
		ReportDesignHandle reportDesign = executionContext.getDesign( );
		ReportScriptExecutor
				.handleAfterFactory( reportDesign, executionContext );
	}
	protected void startRender( )
	{
		ReportDesignHandle reportDesign = executionContext.getDesign( );
		ReportScriptExecutor
				.handleBeforeRender( reportDesign, executionContext );
	}
	protected void closeRender( )
	{
		ReportDesignHandle reportDesign = executionContext.getDesign( );
		ReportScriptExecutor.handleAfterRender( reportDesign, executionContext );
	}
	
	public void setDataSource( IDocArchiveReader dataSource )