Returns an empty PermissionCollection for a given Permission object, or null if
one is not defined. Subclasses of class Permission should
override this if they need to store their permissions in a particular
PermissionCollection object in order to provide the correct semantics
when the {@code PermissionCollection.implies} method is called.
If null is returned,
then the caller of this method is free to store permissions of this
type in any PermissionCollection they choose (one that uses a Hashtable,
one that uses a Vector, etc).
@return a new PermissionCollection object for this type of Permission, or
null if one is not defined.
Returns an empty PermissionCollection for a given Permission object, or null if one is not defined. Subclasses of class Permission should override this if they need to store their permissions in a particular PermissionCollection object in order to provide the correct semantics when the {@code PermissionCollection.implies} method is called. If null is returned, then the caller of this method is free to store permissions of this type in any PermissionCollection they choose (one that uses a Hashtable, one that uses a Vector, etc).
@return a new PermissionCollection object for this type of Permission, or null if one is not defined.