accept undefined config value

Author: zoran995

lib/Models/TerriaConfig.ts

@@ -368,14 +368,13 @@ export class TerriaConfig {
 
   /**
    * Merges `partial` into this config. Only fields present in
-   * `ConfigParameters` are accepted; `undefined` values do not overwrite
-   * existing values.
+   * `ConfigParameters` are accepted.
    */
   @action
   update(partial: Partial<ConfigParameters>): void {
     (Object.entries(partial) as [keyof TerriaConfig, unknown][]).forEach(
       ([key, value]) => {
-        if (key in this && value !== undefined) {
+        if (key in this) {
           (this as any)[key] = value;
         }
       }

test/Models/TerriaConfigSpec.ts

@@ -42,13 +42,6 @@ describe("TerriaConfig", function () {
       expect(config.supportEmail).toBe("[email protected]"); // default unchanged
     });
 
-    it("does not overwrite existing value when undefined is applied", function () {
-      const config = new TerriaConfig();
-      config.update({ appName: undefined });
-
-      expect(config.appName).toBe("TerriaJS App");
-    });
-
     it("uses last value when the same field is applied twice", function () {
       const config = new TerriaConfig();
       config.update({ appName: "First" });