When using constructor binding, if no properties are bound to
a nested property, the top-level instance will be created with a
null value for the nested property.
This commit introduces support for an empty `@DefaultValue` which
indicates that an instance of the nested property must be created
even if nothing is bound to it. It honors any `@DefaultValue`
annotations that the nested property might have in its constructor.
Closes gh-18917
af6d538781