Determine if SQL CMD variable is defined

begin try
	-- do a test to see if this sql cmd variable has been defined.
	IF (N'$(WebServer)' = N'')
	begin
		NoOpTest1:
	end
end try
begin catch
	-- if we had an error, it means the variables have not yet been set.
	-- Set them now.
	:setvar WebServer "www.myserver.com"
	:setvar Environment "live"
end catch