Permutation max = 0 at stringent t-thresholds

[victoris93]

In nbs_bct permutation max appears to always return 0 with the following args:
pvals, adj, null_dist = nbs_bct(scz, controls, thresh=20, tail='both', k = 100, verbose = True, seed = None)
The output is the following:

max component size is 8404
estimating null distribution with 100 permutations
permutation 1 of 100.  Permutation max is 0.0.  Observed max is 8404.0.  P-val estimate is 0.000
permutation 2 of 100.  Permutation max is 0.0.  Observed max is 8404.0.  P-val estimate is 0.000
permutation 3 of 100.  Permutation max is 0.0.  Observed max is 8404.0.  P-val estimate is 0.000

Is the behaviour expected? The connectivity matrix is 1000x1000 (Schaefer 2018).