Vaadin Framework version: 8, all versions

There is a major error in the class com.vaadin.server.VaadinSession (and possibly other classes too, if this is some kind of cargo cult programming in the Vaadin team)

Most public methods in the class use assertions to "check" if the session has the lock. This is fundamentally wrong. Assertions are the wrong tool to check preconditions in public meth

For use cases of conditional cell content, it would be helpful to render empty Div in ComponentRenderer and IconRenderer when given null value.

This is request for convenience and improved DX. It is possible to give empty Div already now as a component.

https://vaadin.com/forum/thread/17439129/grid-icon-column

The reinitializeSession is a helper that the application can use to change the user's session id in order to protect against session fixation attacks. It works by extracting all contents of the old session, invalidating it and then populating the original content into a new session.

This whole procedure is redundant as of Servlet 3.1 which introduced the servletRequest.changeSessionId() met

The following methods/functionality need to be tested:

• Test that findById() successfully returns the correct CustomShelf when a valid ID is passed in
• A null pointer exception is thrown if a null CustomShelf is pased into delete()
• A custom shelf can be successfully deleted
• findAll() gets all custom shelves
• findAll(String shelfName) returns a list of all custom shelves if

Minor adjustment: when creating a SplitLayout, the only constructor overloads are for no parameters or primary/secondary Component. It would make sense to have a constructor that takes Orientation as well (there used to be separate Horizontal and VerticalSplitLayout components).