def parse_subcluster(data_dict):
    """Retrieve Subcluster from PhagesDB.

    If for some reason no cluster info is added at the time
    the genome is added to PhagesDB, 'psubcluster' may automatically be
    set to NULL, which gets returned as None.
    If the phage is a Singleton, 'psubcluster' is None.
    If the phage is clustered but not subclustered, 'psubcluster' is None.
    If the phage is clustered and subclustered, 'psubcluster'
    is a dictionary, and one key is the Subcluster data.

    :param data_dict: Dictionary of data retrieved from PhagesDB.
    :type data_dict: dict
    :returns: Subcluster of the phage.
    :rtype: str
    """
    try:
        if data_dict['psubcluster'] is None:
            subcluster = 'none'
        else:
            subcluster = data_dict['psubcluster']['subcluster']
    except:
        subcluster = ''
    return subcluster
