## Why is this an issue?

Spring provides two options to mark a REST parameter as optional:

1. Use `required = false` in the `@PathVariable` or `@RequestParam` annotation of the respective method parameter or
2. Use type `java.util.Optional<T>` for the method parameter

When using 1., the absence of the parameter, when the REST function is called, is encoded by `null`, which can only be used for object types. If `required = false` is used for a parameter with a primitive and the REST function is called without the parameter, a runtime exception occurs because the Spring data mapper cannot map the `null` value to the parameter.

## How to fix it

Replace primitive types, such as `boolean`, `char`, `int`, with the corresponding wrapper type, such as `Boolean`, `Character`, `Integer`.

Alternatively, you might choose to remove `required = false` from the annotation and use an `Optional<T>` type for the parameter, such as `Optional<Boolean>` or `Optional<String>`, which automatically makes the REST parameter optional. This is the preferred approach because it enforces the proper handling of `null` in the method implementation.

### Code examples

#### Noncompliant code example

    @RequestMapping(value = {"/article", "/article/{id}"})
    public Article getArticle(@PathVariable(required = false) int articleId) { // Noncompliant, null cannot be mapped to int
       //...
    }

#### Compliant solution

    @RequestMapping(value = {"/article", "/article/{id}"})
    public Article getArticle(@PathVariable(required = false) Integer articleId) { // Compliant
       //...
    }

#### Noncompliant code example

    @RequestMapping(value = {"/article", "/article/{id}"})
    public Article getArticle(@PathVariable(required = false) int articleId) { // Noncompliant, null cannot be mapped to int
       //...
    }

#### Compliant solution

    @RequestMapping(value = {"/article", "/article/{id}"})
    public Article getArticle(@PathVariable Optional<Integer> articleId) { // Compliant and preferred approach
       //...
    }

## Resources

### Documentation

- Spring Framework API - Annotation Interface PathVariable

### Articles & blog posts

- Baeldung - Spring Optional Path Variables