TypeScript has disctinct nullable and non-null types if you enable `strictNullChecks` or `strict` in TSConfig (https://www.typescriptlang.org/tsconfig/#strictNullChecks).

In fact, part of the implementation (or at least ideas) were borrowed from TypeScript. Nullability in C# changes depending on the checks around the code (similar to how the type of expressions in ThpeScript can change depending on prior code).