TSQL - Get the earlier of two given dates

/*

       -- Execution

       select dbo.getLowestDate( '1/31/2012', '8/30/2012' );

       select dbo.getLowestDate( '1/31/2012', null );

       select dbo.getLowestDate( null, '8/30/2012' );

       select dbo.getLowestDate( null, null );

*/

ALTER function [dbo].[getLowestDate](

       @date1 date

       , @date2 date

)

returns date

as

begin

       return(

              case when isnull(@date1,'12/31/2099') <= isnull(@date2,'12/31/2099') then @date1 else @date2 end

       );

end

;