handle undefined network_manager.disable
diff --git a/linux/network/interface.sls b/linux/network/interface.sls
index 2fce2b2..955d06e 100644
--- a/linux/network/interface.sls
+++ b/linux/network/interface.sls
@@ -211,7 +211,7 @@
 
 {%- endif %}
 
-{%- if network.network_manager.disable == True %}
+{%- if network.network_manager.disable is defined and network.network_manager.disable == True %}
 NetworkManager:
   service.dead:
   - enable: false