nested exception is java.lang.IllegalStateException: PathVariable annotation was empty on param 1.

This exception occurs when using the PathVariable annotation in a Spring MVC controller method parameter and the annotation value is empty. The PathVariable annotation is used to map a part of the URL to a method parameter.

For example, consider the following URL: /users/{id}. The value in curly braces ({id}) is a path variable that can be mapped to a method parameter using the PathVariable annotation.

If the PathVariable annotation value is empty, as shown below, the exception will be thrown:

@GetMapping("/users/{id}")
public User getUser(@PathVariable("") String id) {
// implementation
}

To fix the issue, provide a non-empty value for the PathVariable annotation, such as:

@GetMapping("/users/{id}")
public User getUser(@PathVariable("id") String id) {
// implementation
}

This will map the value of the {id} path variable to the id method parameter.