Default values and optional settings?

Short answer: Use default values in POCOs or fallback logic: public class MySettings {

Example code

public string ApiKey { get; set; } = "default-api-key";
} Or: var apiKey = config["MySettings:ApiKey"] ?? "fallback";

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.