TypeScript's Strict Null Checks Won't Save You From Runtime Crashes

A developer discovered that enabling strict null checks in TypeScript is not enough to prevent null-related runtime errors, even when code compiles cleanly without warnings. The core issue is that the TypeScript compiler validates static types but cannot verify the actual shape of data arriving from external sources like APIs, databases, or HTTP headers. Two specific failure patterns are highlighted: assertion functions that log warnings instead of throwing errors, causing TypeScript to trust a false type contract, and third-party library type definitions that do not accurately reflect real runtime return values. The article uses a Next.js and Prisma ORM stack as a practical reference to illustrate where the compiler silently approves code that later fails in production. The author argues that true null safety requires runtime validation at system boundaries, treating the compiler as only the first layer of defense.