diff --git a/core/src/main/java/hudson/model/User.java b/core/src/main/java/hudson/model/User.java
index 55bcce97a902a3ad76d40f39ea04cdde6edc2408..a7b622ad4ea19730279df09398a69d1ba0137904 100644
--- a/core/src/main/java/hudson/model/User.java
+++ b/core/src/main/java/hudson/model/User.java
@@ -139,6 +139,9 @@ public class User extends AbstractModelObject {
     }
 
 
+    public static User getUnknown() {
+        return get("unknown");
+    }
 
     public static User get(String name) {
         if(name==null)
diff --git a/core/src/main/java/hudson/scm/CVSChangeLogSet.java b/core/src/main/java/hudson/scm/CVSChangeLogSet.java
index 961291076bdf2a19a751f2755036a95a7f6642cb..12de6bd598e408fbfd4181a708af178f7b9abc1e 100644
--- a/core/src/main/java/hudson/scm/CVSChangeLogSet.java
+++ b/core/src/main/java/hudson/scm/CVSChangeLogSet.java
@@ -147,6 +147,8 @@ public final class CVSChangeLogSet extends ChangeLogSet<CVSChangeLog> {
 
         @Exported
         public User getAuthor() {
+            if(author==null)
+                return User.getUnknown();
             return author;
         }
 
diff --git a/core/src/main/java/hudson/scm/SubversionChangeLogSet.java b/core/src/main/java/hudson/scm/SubversionChangeLogSet.java
index bd816467a9f1d2f280abd143f4a00c43bb4560a3..45b0a9fc8d668e317e81be5b9176abb434506cd7 100644
--- a/core/src/main/java/hudson/scm/SubversionChangeLogSet.java
+++ b/core/src/main/java/hudson/scm/SubversionChangeLogSet.java
@@ -92,6 +92,8 @@ public final class SubversionChangeLogSet extends ChangeLogSet<LogEntry> {
 
         @Override
         public User getAuthor() {
+            if(author==null)
+                return User.getUnknown();
             return author;
         }