Quick Bug Fix Needed – ASP.NET Core Application

Hi everyone I need a small, well-defined bug fixed in an existing ASP.NET Core application. This is a quick task for a developer with strong experience in C# and the ASP.NET Core framework. The issue: One of my API endpoints (POST /api/orders) returns a 500 Internal Server Error when the request body includes an optional field left null. It works fine when all fields are populated, but fails as soon as discountCode is omitted or null. The stack trace points to a NullReferenceException somewhere in the service layer, but I haven't been able to pin down exactly where. Tech stack: ASP.NET Core 8.0 Web API Entity Framework Core SQL Server What I'll provide: Access to the relevant code (private GitHub repo) Steps to reproduce the bug (sample request payload) Full stack trace and error logs What I need: The bug identified and fixed Brief explanation of the root cause and your fix Confirmation that existing functionality isn't broken Requirements: Solid experience with ASP.NET Core and C# Familiarity with EF Core and API validation patterns Available for a fast turnaround To apply, please include: A one-line note on similar ASP.NET Core bugs you've resolved Your estimated time to complete this Thanks