Skip CLI options that don't have an associated config key when buildi…

…ng the config override object

lib/unity_cache_server.js

@@ -87,7 +87,7 @@ class UnityCacheServer {
             if(!cmd.hasOwnProperty(optionKey) || cmd[optionKey] == null) continue;
             const optionVal = cmd[optionKey];
             const configKey = optionMap[optionKey].configKey;
-            _.set(overrides, configKey, optionVal);
+            if(configKey) _.set(overrides, configKey, optionVal);
         }
 
         process.env.NODE_CONFIG = JSON.stringify(overrides);