efmtool python wrapper not finding any EFMs

Hi, I'm trying to use the python wrapper of efmtool to get the EFMs of a toy model but I get the error ValueError: need at least one array to concatenate.

My code is:

import numpy as np

import efmtool

S = np.array([ [1, -1, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 1, -1, 0, -1, 1, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 1, 1, -1, -1, -1, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 1, -1, 1, -1, 0, 0, 0], [0, 0, 0, 0, 0, 0, 1, 0, 0, 0, -1, 0, 0, 1], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, 0, 0], [0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 1, -1, 0,], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, -1], ])

efms = efmtool.calculate_efms(S,np.zeros(len(S[0])),["r_%s" %(i+1) for i in range(len(S[0]))],["m_%s" %(i+1) for i in range(len(S))])

Any help would be much appreciated!

Hettie