def _create_keys_string(entity, keys) -> str:
    """Create formatted string for requested keys if non-null in entity.
    :param Dict entity: entity to check against, eg a Disease or Statement
    :param Tuple keys: key names to check
    :return: formatted String for use in Cypher query
    """
    nonnull_keys = [f"{key}:${key}"
                    for key in keys if entity.get(key)]
    keys_string = ', '.join(nonnull_keys)
    return keys_string