def METHOD_NAME(drugbank_id):
    """Return a mapping for a DrugBank ID to CHEMBL.
    Parameters
    ----------
    drugbank_id : str
        DrugBank ID to map.
    Returns
    -------
    str or None
        The ID mapped to CHEMBL or None if not available.
    """
    return get_db_mapping(drugbank_id, 'CHEMBL')