chore: fix bug

src/common/transformers/decimal.transformer.ts

@@ -11,8 +11,10 @@ export class DecimalTransformer implements ValueTransformer {
   //   return new Decimal(value).toNumber();
   // }
 
-  to(value: Decimal | null): string | null {
-    return value ? value.toString() : "0";
+  to(value: Decimal | number | null): string | null {
+    if (value === null) return "0";
+
+    return value instanceof Decimal ? value.toString() : new Decimal(value).toString();
   }
 
   from(value: string | null): number {