Nulls, often referred to as the "billion-dollar mistake," pose significant challenges in programming, leading to bugs when not properly managed. To address this, TypeScript's strictNullChecks compiler flag treats null and undefined as distinct types, ensuring they are appropriately handled and reducing related errors. However, enabling this feature in an existing codebase can be complex, potentially resulting in thousands of errors that need methodical resolution. Various strategies can be employed to implement strict nulls incrementally, such as using multiple tsconfig files or the non-null assertion operator, each with its pros and cons. The text discusses lessons learned from converting a codebase to be strict null compliant, such as narrowing types early, handling resource differences, and using defaults to manage optional parameters. It concludes that while starting with strict TypeScript rules is ideal for new projects, existing codebases require careful planning and effort, but the benefits of reduced complexity and improved reliability make it worthwhile.