why count is None?

[fenglupeter]

python ~/Massive-PotreeConverter/pympc/get_info.py -i ~/mpc -c 2
Input folder: ~/mpc
Number of processes: 2
Target tile number of points: 5000000000
Target OctTree node number of points: 60000
Starting get_info.py...
lasinfo ~/mpc/points_999_1001_100.las -nc -nv -nco
lasinfo /mpc/points_999_1014_140.las -nc -nv -nco
lasinfo /mpc/points_999_999_620.las -nc -nv -nco
Execution failed!
Traceback (most recent call last):
File "/Massive-PotreeConverter/pympc/get_info.py", line 84, in main
run(args.input, args.proc, args.avgtile, args.avgnode)
File "/Massive-PotreeConverter/pympc/get_info.py", line 9, in run
(_, tcount, tminx, tminy, tminz, tmaxx, tmaxy, tmaxz, _, _, _) = utils.getPCFolderDetails(inputFolder, numberProcs)
File "/root/py3/lib/python3.5/site-packages/pympc/utils.py", line 139, in getPCFolderDetails
tcount += count
TypeError: unsupported operand type(s) for +=: 'int' and 'NoneType'

lasinfo ~/mpc/points_999_1002_120.las -nc -nv -nco