Unless I am missing something, it is not possible to update or insert an empty string or null using the sql:param tag, because it explicitly does not allow use with an empty value. This is a serious shortcoming! Also, the SQL standard differentiates between the empty string and null, although Oracle conflates the two, so for ANSI compliant databases, there should also be a way to set null parameters with the sql:param tag.
Fixed. Null parameter values set to SQL value null.