How to add non-nullable columns with default values

IF NOT EXISTS (SELECT * FROM sys.columns WHERE object_id=OBJECT_ID('[caConfig]') AND [Name]='ExportWizardVersion')
ALTER TABLE [caConfig]
    ADD
		[ExportWizardVersion] varchar(5) not null CONSTRAINT DF_caConfig_ExportWizardVersion DEFAULT '5.8' WITH VALUES,
		[ExportPeriodEnd] varchar(10) not null CONSTRAINT DF_caConfig_ExportPeriodEnd DEFAULT 'MonthEnd' WITH VALUES