Empty validation exception

pls note I had to remove final in order to facilitate overriding
in the ifc and allowing me to not add anything to the list of msgs

Author: hub-cap

client/rest-high-level/src/main/java/org/elasticsearch/client/Validatable.java

@@ -22,6 +22,10 @@
  * Defines a validation layer for Requests.
  */
 public interface Validatable {
+    ValidationException EMPTY_VALIDATION = new ValidationException() {
+        @Override
+        public void addValidationError(String error) { }
+    };
 
     /**
      * Perform validation. This method does not have to be overridden in the event that no validation needs to be done.
@@ -30,6 +34,6 @@ public interface Validatable {
      * {@link ValidationException} that contains a list of all failed validation.
      */
     default ValidationException validate() {
-        return new ValidationException();
+        return EMPTY_VALIDATION;
     }
 }

client/rest-high-level/src/main/java/org/elasticsearch/client/ValidationException.java

@@ -31,7 +31,7 @@ public class ValidationException extends IllegalArgumentException {
      * Add a new validation error to the accumulating validation errors
      * @param error the error to add
      */
-    public final void addValidationError(String error) {
+    public void addValidationError(String error) {
         validationErrors.add(error);
     }