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
{
		ParameterValidationException engineException;
		boolean visitScalarParameter( ScalarParameterHandle param,
				Object value )
		{
			try
			{
				return validateScalarParameter( param );
			}
			catch ( ParameterValidationException pe )
			{
				engineException = pe;
			}
			return false;
		}
		boolean visitParameterGroup( ParameterGroupHandle group,
				Object value )
		{
			return visitParametersInGroup( group, value );
		}
	};
	protected void loggerParamters( )
	{
		if ( log.isLoggable( Level.FINE ) )
		{
			final StringBuffer buffer = new StringBuffer( );
			
			new ParameterVisitor( ) {
				boolean visitScalarParameter( ScalarParameterHandle param,
						Object value )