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
{
		String paramName = paramHandle.getName( );
		Object paramValue = runValues.get( paramName );
		String type = paramHandle.getDataType( );
		
		if ( paramValue == null )
		{
			if ( !paramHandle.isRequired( ) )
				return true;
			throw new ParameterValidationException(
					MessageConstants.NULL_PARAMETER_EXCEPTION,
					new String[]{paramName} );
		}
		String source = paramHandle.getValidate( );
		if ( source != null && source.length( ) != 0 )
		{
			Object result = executionContext.evaluate( source );
			if ( !( result instanceof Boolean )
					|| !( (Boolean) result ).booleanValue( ) )
			{
				throw new ParameterValidationException(
						MessageConstants.NULL_PARAMETER_EXCEPTION,
						new String[]{paramName, source} );
			}
		}
		
		String paramType = paramHandle.getParamType( );
		if ( DesignChoiceConstants.SCALAR_PARAM_TYPE_MULTI_VALUE
				.equals( paramType ) )
		{