C# "CS8600: converting null literal to non-nullable type" in CI

CS8600 means a null or possibly-null value is being assigned to a variable typed as non-nullable. With nullable enabled and warnings as errors, CI fails on it. It is the compiler telling you the static null-flow does not prove non-nullness.

What this error means

The build fails with CS8600 at the assignment. It is deterministic and frequently CI-only because of warnings-as-errors.

dotnet

Parsing.cs(15,13): error CS8600: Converting null literal or possible null value to
non-nullable type.

Common causes

A possibly-null result assigned to a non-nullable variable

A method returning a nullable reference (e.g. a dictionary TryGet pattern or FirstOrDefault) is stored in a non-nullable local without a null check.

CI treats nullable warnings as errors

The build pipeline enables warnings-as-errors, so this otherwise-warning fails CI.

How to fix it

Make the nullability explicit

Declare the local as nullable (string?) and handle the null branch.
Or guard with a null check / null-forgiving ! only when you can prove non-null.
Rebuild.

string? name = items.FirstOrDefault();
if (name is null) return;

How to prevent it

Keep nullable reference types enabled throughout the codebase.
Prefer pattern-based null checks over null-forgiving operators.