Was your schema defined by Hibernate? Or did you define it yourself?

AFAICS, Hibernate should generate a schema with the boolean data type. Is this type supported by SQL Anywhere? Does it support null?

From what I can see here http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc38151.1602/doc/html/san1278452921678.html , bit only supports 0 or 1, not null. So I'm a bit confused about what you're saying.