def get_ocw_topics(topics_collection):
    """
    Extracts OCW topics and subtopics and returns a unique list of them

    Args:
        topics_collection (dict): The JSON object representing the topic

    Returns:
        list of str: list of topics
    """
    topics = []

    for topic_object in topics_collection:
        if topic_object["ocw_feature"]:
            topics.append(topic_object["ocw_feature"])
        if topic_object["ocw_subfeature"]:
            topics.append(topic_object["ocw_subfeature"])
        if topic_object["ocw_speciality"]:
            topics.append(topic_object["ocw_speciality"])

    return list(set(topics))