Fetches custom metadta for an already exisiting Video.

def get_custom_metadata(self):
        """
        Fetches custom metadta for an already exisiting Video.
        """
        if self.id is not None:
            data = self.connection.get_item(
                'find_video_by_id',
                video_id=self.id,
                video_fields="customFields"
            )
            for key in data.get("customFields", {}).keys():
                val = data["customFields"].get(key)
                if val is not None:
                    self.add_custom_metadata(key, val)