def _compare_items(a, b):
    """
    Compares the items of the specified nodes.

    In particular, this function will:
        - return True if both nodes are null.
        - return False if one node is null and the other is not.
        - return the comparison of each node's items, otherwise.

    :param a: A node to compare.
    :param b: Another node to compare.
    :return: Whether or not the items of two nodes are equivalent.
    """
    if a is None and b is None:
        return True
    elif (a is None and b is not None) or (a is not None and b is None):
        return False
    return a.item == b.item