def get_first_minimum(values, tolerance):
    """Find the first minimum.

    Return first value from list *values* for which the next values
    increase by more than *tolerance* or return None when no maximum can be
    identified. Restart searching after a value which is None.

    Parameters
    ----------
    values: list of float
    tolerance: float

    Returns
    -------
    result: float or None

    """
    valuemin = None
    for value in values:
        if value is None:
            valuemin = None
            continue
        if valuemin is None or value < valuemin:
            valuemin = value
        elif valuemin < value - tolerance:
            return valuemin
    return None
