fix: mapping part of url if null or empty

src/api/api.service.ts

@@ -52,7 +52,7 @@ export default abstract class ApiService {
   }
 
   private static combineUrls(...parts: string[]): string {
-    return parts.map(part => part.replace(/(^\/+|\/+$)/g, '')).join('/');
+    return parts.map(part => (!part || part == '' ? '/' : part).replace(/(^\/+|\/+$)/g, '')).join('/');
   }
 
   protected combinedUrl(request: RequestData) {