sybase 12.5 insert null values

It's weird that sybase will convert empty string into ' ' (note: not empty but just a whitespace). 

So if you want to insert a null into a row, you should do like this:

insert tabe xxx values (..., null, ...)

That's, include a null value in your sql query, or you should not metion that column name in the sql, it defaultly will insert a null.