minor refactoring and more config util assertions

src/config/config.util.ts

@@ -7,21 +7,38 @@ import { hasNoValue } from '../app/shared/empty.util';
 import { AppConfig } from './app-config.interface';
 import { ThemeConfig } from './theme.model';
 
+/**
+ * Extend Angular environment with app config.
+ *
+ * @param env       environment object
+ * @param appConfig app config
+ */
 const extendEnvironmentWithAppConfig = (env: any, appConfig: AppConfig): void => {
   mergeConfig(env, appConfig);
   console.log(`Environment extended with app config`);
 };
 
-const mergeConfig = (config: any, appConfig: AppConfig): void => {
+/**
+ * Merge one config into another.
+ *
+ * @param destinationConfig destination config
+ * @param sourceConfig      source config
+ */
+const mergeConfig = (destinationConfig: any, sourceConfig: AppConfig): void => {
   const mergeOptions = {
     arrayMerge: (destinationArray, sourceArray, options) => sourceArray
   };
-  Object.assign(config, merge.all([
-    config,
-    appConfig
+  Object.assign(destinationConfig, merge.all([
+    destinationConfig,
+    sourceConfig
   ], mergeOptions));
 };
 
+/**
+ * Get default them config from environment.
+ *
+ * @returns default theme config
+ */
 const getDefaultThemeConfig = (): ThemeConfig => {
   return environment.themes.find((themeConfig: any) =>
     hasNoValue(themeConfig.regex) &&