SQL Query Syntax

Hello Experts,

I am using SyBAse SQL Anywhere v10. This is my query

select top(1) CASHTIPS from TipPool where opendate = 20150601 order by LASTUPDATE desc

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This works great except if CASHTIPS value is null, it returns a "0". I would like to return NULL if the result is NULL. I have tried to use case when but I cant figure out how to use that in conjunction with top

Thanks!