def mul_or_none(a, b):
    """Return the element wise multiplicative of the inputs.
    If either input is None, we return None.

    Parameters
    ----------
    a
        A tensor input.
    b
        Another tensor input with the same type as a.

    Returns
    -------
    None if either input is None. Otherwise returns a * b.
    """
    if a is None or b is None:
        return None
    return a * b