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
{
		boolean visitParametersInGroup( ParameterGroupHandle group, Object value )
		{
			SlotHandle parameters = group.getParameters( );
			Iterator iter = parameters.iterator( );
			while ( iter.hasNext( ) )
			{
				Object param = iter.next( );
				if ( param instanceof CascadingParameterGroupHandle )
				{
					if ( !visitCascadingParamterGroup(
							(CascadingParameterGroupHandle) param, value ) )
					{
						return false;
					}
				}
				else if ( param instanceof ParameterGroupHandle )
				{
					if ( !visitParameterGroup( (ParameterGroupHandle) param,
							value ) )
					{
						return false;