isolated nodes not counted as components

[VincenzoPerri]

Running the code:

tr_net = pp.Network()
for i in range(n):
    tr_net.add_node(i)

For n <= 2 we get:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-84-329b4db68bec> in <module>
----> 1 pp.algorithms.components.connected_components(tr_net)

/opt/tljh/user/lib/python3.6/site-packages/pathpy/algorithms/components.py in connected_components(network, lanczos_vecs, maxiter)
     48     if maxiter is None:
     49         maxiter = n*10
---> 50     vals, vecs = _sla.eigs(L, k=n, which="SM", return_eigenvectors=True)
     51 
     52     components = defaultdict(set)

/opt/tljh/user/lib/python3.6/site-packages/scipy/sparse/linalg/eigen/arpack/arpack.py in eigs(A, k, M, sigma, which, v0, ncv, maxiter, tol, return_eigenvectors, Minv, OPinv, OPpart)
   1247 
   1248     if k <= 0:
-> 1249         raise ValueError("k=%d must be greater than 0." % k)
   1250 
   1251     if k >= n - 1:

ValueError: k=0 must be greater than 0.

While for n>2 we get the following:
defaultdict(set, {})

Our expectation would have been to get the isolated nodes as components.