Always validate that values exist and have expected properties before accessing them, especially when removing non-null assertions or performing type casting. Avoid making assumptions about value presence or type safety without explicit checks. Key practices: - When removing non-null assertion operators (!), add explicit null/undefined checks - Validate input types before casting, especially with schema validation libraries - Use specific filtering logic instead of generic Boolean filtering that may exclude valid falsy values - Consider whether to pass empty objects vs undefined parameters based on actual usage Example from the discussions: ```typescript // Risky - assumes route exists after removing non-null assertion const route = this.looseRoutesById[d.routeId] // Better - validate before use const route = this.looseRoutesById[d.routeId] if (!route) return // Risky - Boolean filter excludes valid falsy numbers like 0, -1 paths.filter(Boolean).join('/') // Better - explicit check for meaningful values paths.filter((val) => val !== undefined && val !== null).join('/') ``` This prevents runtime errors from null reference exceptions and ensures code behaves correctly with edge case values.