made use of first class citizen objects as json validator functions

backend-dart/lib/infrastructure/persistence/prisma_user_data_source.dart

@@ -45,9 +45,13 @@ class PrismaUserDataSource implements UserDataSource {
         message: 'Failed to find user by email: ${error.toString()}',
       ),
     )
-        .flatMap(errorOnNull(AppError.notFound(
-          'User with email $email found',
-        )))
+        .flatMap(
+          errorOnNull(
+            AppError.notFound(
+              'User with email $email found',
+            ),
+          ),
+        )
         .flatMap(mapper.from);
   }
 
@@ -63,9 +67,13 @@ class PrismaUserDataSource implements UserDataSource {
         message: 'Failed to find user by ID: ${error.toString()}',
       ),
     )
-        .flatMap(errorOnNull(AppError.notFound(
-          "User with id $id not found",
-        )))
+        .flatMap(
+          errorOnNull(
+            AppError.notFound(
+              "User with id $id not found",
+            ),
+          ),
+        )
         .flatMap(mapper.from);
   }
 
@@ -104,15 +112,24 @@ class PrismaUserDataSource implements UserDataSource {
   }
 
   @override
-  TaskEither<IError, void> delete(String id) {
-    return TaskEither.tryCatch(
+  TaskEither<IError, User> delete(String id) {
+    return TaskEither<IError, UserDbo?>.tryCatch(
       () async {
-        await prisma.userDbo.delete(where: UserDboWhereUniqueInput(id: id));
+        return await prisma.userDbo
+            .delete(where: UserDboWhereUniqueInput(id: id));
       },
       (error, _) => AppError.databaseError(
         message: 'Failed to delete user: ${error.toString()}',
       ),
-    );
+    )
+        .flatMap(
+          errorOnNull(
+            AppError.notFound(
+              'User not found',
+            ),
+          ),
+        )
+        .flatMap(mapper.from);
   }
 
   @override