Fixed issue unmarhalling merge_request system hook events (#332).

src/main/java/org/gitlab4j/api/systemhooks/MergeRequestSystemHookEvent.java

@@ -2,21 +2,18 @@ package org.gitlab4j.api.systemhooks;
 
 import org.gitlab4j.api.webhook.MergeRequestEvent;
 
-import com.fasterxml.jackson.annotation.JsonIgnore;
-import com.fasterxml.jackson.annotation.JsonSubTypes;
-import com.fasterxml.jackson.annotation.JsonTypeInfo;
-
-@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, property="object_kind")
-@JsonSubTypes({
-    @JsonSubTypes.Type(value = MergeRequestSystemHookEvent.class, name = MergeRequestSystemHookEvent.OBJECT_KIND),
-})
 public class MergeRequestSystemHookEvent extends MergeRequestEvent implements SystemHookEvent {
 
     public static final String X_GITLAB_EVENT = "System Hook";
+    public static final String MERGE_REQUEST_EVENT = "merge_request";
+
+    @Override
+    public String getObjectKind() {
+        return (MERGE_REQUEST_EVENT);
+    }
 
-    @JsonIgnore
     @Override
     public String getEventName() {
-        return (OBJECT_KIND);
+        return (MERGE_REQUEST_EVENT);
     }
 }

src/main/java/org/gitlab4j/api/systemhooks/SystemHookEvent.java

@@ -26,7 +26,8 @@ import com.fasterxml.jackson.annotation.JsonTypeInfo;
     @JsonSubTypes.Type(value = RemoveGroupMemberSystemHookEvent.class, name = GroupMemberSystemHookEvent.GROUP_MEMBER_REMOVED_EVENT),
     @JsonSubTypes.Type(value = PushSystemHookEvent.class, name = PushSystemHookEvent.PUSH_EVENT),
     @JsonSubTypes.Type(value = TagPushSystemHookEvent.class, name = TagPushSystemHookEvent.TAG_PUSH_EVENT),
-    @JsonSubTypes.Type(value = RepositorySystemHookEvent.class, name = RepositorySystemHookEvent.REPOSITORY_UPDATE_EVENT)
+    @JsonSubTypes.Type(value = RepositorySystemHookEvent.class, name = RepositorySystemHookEvent.REPOSITORY_UPDATE_EVENT),
+    @JsonSubTypes.Type(value = MergeRequestSystemHookEvent.class, name = MergeRequestSystemHookEvent.MERGE_REQUEST_EVENT)
 })
 public interface SystemHookEvent {
 

src/main/java/org/gitlab4j/api/systemhooks/SystemHookManager.java

@@ -16,6 +16,7 @@ import org.gitlab4j.api.utils.HttpRequestUtils;
 import org.gitlab4j.api.utils.JacksonJson;
 
 import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;
 
 /**
  * This class provides a handler for processing GitLab System Hook callouts.
@@ -90,11 +91,14 @@ public class SystemHookManager extends HookManager {
                 tree = jacksonJson.readTree(reader);
             }
 
-            if (tree.has("object_kind")) {
+            // NOTE: This is a hack based on the GitLab documentation showing that the "event_name" property
+            // is missing from the merge_request system hook event
+            if (!tree.has("event_name") && tree.has("object_kind")) {
                 String objectKind = tree.asText("object_kind");
                 switch (objectKind) {
-                    case MergeRequestSystemHookEvent.OBJECT_KIND:
-                        event = jacksonJson.unmarshal(MergeRequestSystemHookEvent.class, tree);
+                    case MergeRequestSystemHookEvent.MERGE_REQUEST_EVENT:
+                        ObjectNode node = (ObjectNode)tree;
+                        node.put("event_name", MergeRequestSystemHookEvent.MERGE_REQUEST_EVENT);
                         break;
 
                     default:
@@ -102,11 +106,10 @@ public class SystemHookManager extends HookManager {
                         LOGGER.warning(message);
                         throw new GitLabApiException(message);
                 }
-
-            } else {
-                event = jacksonJson.unmarshal(SystemHookEvent.class, tree);
             }
 
+            event = jacksonJson.unmarshal(SystemHookEvent.class, tree);
+
             if (LOGGER.isLoggable(Level.FINE)) {
                 LOGGER.fine(event.getEventName() + "\n" + jacksonJson.marshal(event) + "\n");
             }