| Passing a literal `null` to an `Optional` accepting parameter is likely a bug. |
| `Optional` is already designed to encode missing values through a non-`null` |
| instance. |
| |
| ```java |
| Optional<Integer> double(Optional<Integer> i) { |
| return i.map(i -> i * 2); |
| } |
| |
| Optional<Integer> doubled = double(null); |
| ``` |
| |
| ```java |
| Optional<Integer> doubled = double(Optional.empty()); |
| ``` |
| |
| This is a scenario that can easily happen when refactoring code from accepting |
| `@Nullable` parameters to accept `Optional`s. Note that the check will not match |
| if the parameter is explicitly annotated `@Nullable`. |
