Prior to this commit, binding a `@ModelAttribute` object as a Controller
handler paramater would instantiate the object and set all its
properties, fetching data from the request. When no data is available,
the WebDataBinder tries to bind default "empty" values:
* Boolean.FALSE for boolean types
* empty arrays for array types
* null by default
This commit adds the new default empty values:
* empty Collections for Collection types
* empty Maps for Map types
Rather than using empty implementations provided by `Collections.empty`
(which are not mutable), we're using the closest possible target type
and real implementations, provided by the `CollectionFactory`.
Issue: SPR-13502
862d10c128