diff -r 7de2652f7ee8 -r 2f35c2ae7de8 server/src/main/java/org/iri_research/renkan/models/ProjectRevision.java
--- a/server/src/main/java/org/iri_research/renkan/models/ProjectRevision.java	Sun May 18 10:31:12 2014 +0200
+++ b/server/src/main/java/org/iri_research/renkan/models/ProjectRevision.java	Sun May 25 13:45:24 2014 +0900
@@ -3,6 +3,7 @@
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
+import java.util.UUID;
 
 import org.bson.types.ObjectId;
 import org.joda.time.DateTime;
@@ -47,6 +48,9 @@
     public ProjectRevision(ObjectId id, String title, String description,
             String uri, Project project, int revision, Date created) {
         super(id, title, description, uri, null);
+        if(this.id == null) {
+            this.id = new ObjectId();
+        }
         this.project = project;
         this.revision = revision;
         if (created == null) {
@@ -79,5 +83,11 @@
     protected String getRawKeyPart() {
         return Long.toString(this.getCreated().getMillis());
     }
+    
+    @Override
+    protected ObjectId getDefaultId() {
+        return new ObjectId();
+    }
+
 
 }