KEYCLOAK-2136: Unexpected error when trying to create mapper with already existing name

model/jpa/src/main/java/org/keycloak/models/jpa/ClientAdapter.java

@@ -3,6 +3,7 @@ package org.keycloak.models.jpa;
 import org.keycloak.connections.jpa.util.JpaUtils;
 import org.keycloak.models.ClientModel;
 import org.keycloak.models.KeycloakSession;
+import org.keycloak.models.ModelDuplicateException;
 import org.keycloak.models.ProtocolMapperModel;
 import org.keycloak.models.RealmModel;
 import org.keycloak.models.RoleContainerModel;
@@ -328,7 +329,7 @@ public class ClientAdapter implements ClientModel {
     @Override
     public ProtocolMapperModel addProtocolMapper(ProtocolMapperModel model) {
         if (getProtocolMapperByName(model.getProtocol(), model.getName()) != null) {
-            throw new RuntimeException("protocol mapper name must be unique per protocol");
+            throw new ModelDuplicateException("Protocol mapper name must be unique per protocol");
         }
         String id = model.getId() != null ? model.getId() : KeycloakModelUtils.generateId();
         ProtocolMapperEntity entity = new ProtocolMapperEntity();