x = list(range(5))
k = numpy.array([(1.0, 0.001), (1.1, 0.002), (None, None), (1.2, 0.003), (
    0.99, 0.004)])
Fig, ax = pyplot.subplots()
ax.plot(x, k[:, (0)], 'k-')
arr_none = np.array([None])
mask = (k[:, (0)] == arr_none) | (k[:, (1)] == arr_none)
ax.plot(numpy.arange(len(y))[mask], k[mask, 0] + k[mask, 1], 'k--')
matplotlib: построение массивов numpy с None в качестве значений