Remove `None` values from list of networks to scan

Fixes #540

monkey/common/network/network_range.py

@@ -44,9 +44,9 @@ class NetworkRange(object, metaclass=ABCMeta):
 
     @staticmethod
     def get_range_obj(address_str):
-        address_str = address_str.strip()
         if not address_str:  # Empty string
             return None
+        address_str = address_str.strip()
         if NetworkRange.check_if_range(address_str):
             return IpRange(ip_range=address_str)
         if -1 != address_str.find('/'):

monkey/infection_monkey/network/network_scanner.py

@@ -34,6 +34,7 @@ class NetworkScanner(object):
         LOG.info("Found local IP addresses of the machine: %r", self._ip_addresses)
         # for fixed range, only scan once.
         self._ranges = [NetworkRange.get_range_obj(address_str=x) for x in WormConfiguration.subnet_scan_list]
+        self._ranges = list(filter(None, self._ranges))
         if WormConfiguration.local_network_scan:
             self._ranges += get_interfaces_ranges()
         self._ranges += self._get_inaccessible_subnets_ips()