activitypub.Collection: contains_item_with_id type mismatch

[steve-bate]

The contains_item_with_id predicate requires id to be a str, but Collection.contains is iterating over instances of AnyObject returned by self.items().

    def contains(self, matcher: Callable[[AnyObject],bool]) -> bool:
        """
        Returns true if this Collection contains an item, as determined by the
        matcher object. This method passes the members of this collection to the
        matcher one at a time, and the matcher decides when there is a match.
        """
        for item in self.items(): # <-- iterates AnyObject, not str
            if matcher(item):
                return True
        return False

    def contains_item_with_id(self, id: str) -> bool:
        """
        Convenience method that looks for items that are simple object identifiers.
        FIXME: this can be much more complicated in ActivityStreams, but this
        implementation is all we need right now.
        """
        return self.contains(lambda candidate: id == candidate if isinstance(candidate,str) else False) # <-- requires str

# ...

    def items(self) -> Iterator[AnyObject]:
        items = self._delegate.json_field('orderedItems' if self.is_ordered() else 'items')
        if items is not None:
            for item in items:
                if isinstance(item,str):
                    yield AnyObject(item) # <-- not yielding a str
# ...