For now, if the collection element is a component that consists entirely of nullable properties, we will have to forcefully recreate the entire collection. In order to only delete row-by-row as needed, that would require SQL like "WHERE ( COL = ? OR ( COL is null AND ? is null ) )", rather than the current "WHERE COL = ?" (fails for null for most DBs). Note that the params would have to be bound twice. Until we eventually add "parameter bind points" concepts to the AST in ORM 5+, handling this type of condition is either extremely difficult or impossible. Forcing recreation isn't ideal, but not really any other option in ORM 4.