Validating @PathVariable if it is null in Spring Boot app?

In Spring Boot applications, I have problem with validating @PathVariable for long type and even if I tried the following approaches, I cannot validate @PathVariable for null values (whereas I can using @RequestParam):

• Trying to use @Valid and @NotNull annotations before @PathVariable in the controller

• Using primitive type (long instead of Long)

• Adding @Validated annotation to Controller as class level besides using @Valid and @NotNull annotations in the Controller method.

So, here is my Controller method and I am wondering, if it is not possible to validate null path variable? Actually Swagger does not let the user send request with null path variable, but Postman lets.

@GetMapping("/categories/{id}")
public ResponseEntity<ApiResponse<CategoryDto>> findById(@PathVariable long id) {
    // ...
}

Here is the error message after sending null path variable on Postman:

"message": "Failed to convert value of type 'java.lang.String' to required type 'long'; nested exception is java.lang.NumberFormatException: For input string: ":id"" }