diff -dPNur ansible-2.4.3.0/lib/ansible/modules/net_tools/nmcli.py ansible-2.4.3.0-new/lib/ansible/modules/net_tools/nmcli.py
--- ansible-2.4.3.0/lib/ansible/modules/net_tools/nmcli.py	2018-02-01 00:09:48.000000000 +0100
+++ ansible-2.4.3.0-new/lib/ansible/modules/net_tools/nmcli.py	2018-03-12 16:54:08.121892385 +0100
@@ -556,7 +560,7 @@
         self.type=module.params['type']
         self.ip4=module.params['ip4']
         self.gw4=module.params['gw4']
-        self.dns4=' '.join(module.params['dns4'])
+        self.dns4=' '.join(module.params['dns4']) if module.params.get('dns4') else None
         self.ip6=module.params['ip6']
         self.gw6=module.params['gw6']
         self.dns6=module.params['dns6']