def resolve_meta_key(hub, key, meta):
    """ Resolve a value when it's a string and starts with '>' """
    if key not in meta:
        return None
    value = meta[key]
    if isinstance(value, str) and value[0] == '>':
        topic = value[1:]
        if topic not in hub:
            raise KeyError('topic %s not found in hub' % topic)
        return hub[topic].get()
    return value
