Can't figure it out how to

Answer 1

The JSP contains a select tag returned by the action. When you add an order it should have a list attribute bound to the bean property. It should be a top object in the value stack.

In most cases initializing that property in the action class better to implement the preparable interface where you have to write prepare() method and initialize the list.

The exception is thrown because the list attribute of the s:select tag couldn't be null. You should properly initialize the variable used for the tag before returning a result that has references to that variable.