fix

src/common/fall-back.ts

@@ -1,7 +1,13 @@
 type Handler<T> = () => T | Promise<T>;
+type Checker<T> = (result: T) => T | Promise<T>;
 
 export class Fallback<T> {
     private handlers: Handler<T>[] = [];
+    private checker: Checker<T>;
+
+    constructor(checker?: Checker<T>) {
+        this.checker = checker || (async (result: T) => result);
+    }
 
     add(handler: Handler<T>): this {
         this.handlers.push(handler);
@@ -14,8 +20,10 @@ export class Fallback<T> {
         for (const handler of this.handlers) {
             try {
                 const result = await handler();
-                if (result !== undefined) {
-                    return result;
+                try {
+                    return await this.checker(result);
+                } catch (checkerError) {
+                    errors.push(checkerError instanceof Error ? checkerError : new Error(String(checkerError)));
                 }
             } catch (error) {
                 errors.push(error instanceof Error ? error : new Error(String(error)));
@@ -23,4 +31,13 @@ export class Fallback<T> {
         }
         throw new AggregateError(errors, 'All handlers failed');
     }
+}
+export class FallbackUtil{
+    static boolchecker<T>(value: T, condition: boolean): T {
+        if (condition) {
+            return value;
+        } else {
+            throw new Error('Condition is false, throwing error');
+        }
+    }
 }