SONARJAVA-5293 Modify rule S6856 to also cover opposite case (#4619)

rules/S6856/java/rule.adoc

@@ -7,6 +7,8 @@ They are part of the Spring Web module and are commonly used to define the route
 
 If a method has a path template containing a placeholder, like "/api/resource/{id}", and there's no `@PathVariable` annotation on a method parameter to capture the id path variable, Spring will disregard the id variable.
 
+This rule will raise an issue if a method has a path template with a placeholder, but no corresponding `@PathVariable`, or vice-versa.
+
 == How to fix it
 
 === Code examples
@@ -19,6 +21,11 @@ If a method has a path template containing a placeholder, like "/api/resource/{i
 public ResponseEntity<String> getResourceById(Long id) { // Noncompliant - The 'id' parameter will not be automatically populated with the path variable value
   return ResponseEntity.ok("Fetching resource with ID: " + id);
 }
+
+@GetMapping("/api/asset/")
+public ResponseEntity<String> getAssetById(@PathVariable Long id) { // Noncompliant - The 'id' parameter does not have a corresponding placeholder
+  return ResponseEntity.ok("Fetching asset with ID: " + id);
+}
 ----
 
 ==== Compliant solution
@@ -29,6 +36,11 @@ public ResponseEntity<String> getResourceById(Long id) { // Noncompliant - The '
 public ResponseEntity<String> getResourceById(@PathVariable Long id) { // Compliant
   return ResponseEntity.ok("Fetching resource with ID: " + id);
 }
+
+@GetMapping("/api/asset/{id}")
+public ResponseEntity<String> getAssetById(@PathVariable Long id) {
+  return ResponseEntity.ok("Fetching asset with ID: " + id);
+}
 ----
 
 == Resources