Establish consistent null handling patterns at API boundaries to prevent null pointer exceptions and improve code clarity: 1. Validate method parameters using explicit null checks: ```java public void setHttpClient(HttpClient httpClient) { Assert.notNull(httpClient, "HttpClient must not be null"); this.httpClient = httpClient; } ``` 2. Return empty collections instead of null: ```java public List getPropertyAccessors() { return Collections.emptyList(); // Instead of returning null } ``` 3. Use Optional only as a return type, never as a field: ```java // DON'T private Optional errorStatus; // Avoid Optional as field // DO public Optional findUserById(String id) { // OK as return type // ... } ``` 4. For nullable return values in internal APIs, prefer explicit @Nullable annotation over Optional: ```java @Nullable protected Class getReturnType(Method method) { // ... } ``` These patterns ensure consistent null handling, improve code readability, and reduce the likelihood of null-related bugs. They also help maintain clear contracts between components while avoiding unnecessary Optional usage.