When defining configuration schemas, use consistent patterns for safe property access, async resolution, and default value handling. Always use optional chaining with fallback values for nested configuration properties, leverage `$resolve` for complex async configuration logic, and ensure proper backwards compatibility. Key patterns to follow: 1. **Safe property access**: Use optional chaining with fallbacks for nested config properties: ```ts const extraKeys = nuxt.options?.experimental?.extraPageMetaExtractionKeys || [] ``` 2. **Async configuration resolution**: Use `$resolve` for complex configuration logic that requires async operations or cross-property dependencies: ```ts serverDir: { $resolve: async (val: string | undefined, get): Promise => { return resolve(await get('rootDir') as string, val ?? 'server') } } ``` 3. **Default value merging**: Use `defu` for merging configuration objects with proper defaults: ```ts spaLoaderAttrs: { $resolve: (val: undefined | null | Record) => { return defu(val, { id: val?.id ?? '__nuxt-spa-loader', }) } } ``` 4. **Backwards compatibility**: Check for legacy configuration options when introducing new patterns: ```ts propsDestructure: { $resolve: async (val, get) => { // Check both new and legacy locations return val ?? Boolean((await get('vue') as Record).propsDestructure) } } ``` 5. **Runtime config handling**: Distinguish between `undefined` (not set) and `null` (explicitly set to null) values: ```ts // Only filter out undefined, preserve null values for runtime override capability if (typeof obj[key] === 'undefined') { // handle undefined case } ``` This ensures configuration is resolved consistently, safely handles missing values, and maintains backwards compatibility while supporting complex async resolution scenarios.