message: specified that the alg returns None if input is empty
diff: @@ -103,6 +103,7 @@ def lagrangian_barycenter(pdiagset, init=None, verbose=False):
  :param pdiagset: a list of size m containing numpy.array of shape (n x 2)
  (n can variate), encoding a set of
  persistence diagrams with only finite coordinates.
  + If empty, returns None.
  :param init: The initial value for barycenter estimate.
  If None, init is made on a random diagram from the dataset.
  Otherwise, it must be an int
  