Small but important fix for #682:

- MapSwitcher expects an array (as it runs .map() on the property) from backend.
- Also updated the comment in client to better reflect the current state of affairs.

new-backend/server/api/services/config.service.v2.js

@@ -244,7 +244,7 @@ class ConfigServiceV2 {
 
       // Finally, take a look in LayerSwitcher.options and see
       // whether user specific maps are needed. If so, grab them.
-      let userSpecificMaps = null; // Set to null, client looks for this key!
+      let userSpecificMaps = []; // Set to empty array, client will do .map() on it.
       if (mapConfig.map.mapselector === true) {
         userSpecificMaps = await this.getUserSpecificMaps(user);
       }

new-client/src/controls/MapSwitcher.js

@@ -46,11 +46,10 @@ class MapSwitcher extends React.PureComponent {
   componentDidMount() {
     let { proxy, mapserviceBase } = this.appModel.config.appConfig;
 
-    // If user specific maps already exist in config, there's no need
-    // to fetch again (the new API provides this). Please note that
-    // it will be null if map doesn't want to show the map selector -
-    // hence we look for undefined specifically: the old API will not
-    // provide this property at all.
+    // If user specific maps is provided by the new API, the key will
+    // already exist in config and there's no need to fetch again.
+    // However, if it's undefined, it looks like we're using the old API
+    // and MapSwitcher must do the fetch by itself.
     if (this.appModel.config.userSpecificMaps !== undefined) {
       this.handleLoading(this.appModel.config.userSpecificMaps);
     } else {