diff --git a/ReleaseNotes/ReleaseNotes-2.1.2.4.txt b/ReleaseNotes/ReleaseNotes-2.1.2.4.txt
index f511c2719a..c651b69fd4 100644
--- a/ReleaseNotes/ReleaseNotes-2.1.2.4.txt
+++ b/ReleaseNotes/ReleaseNotes-2.1.2.4.txt
@@ -32,6 +32,13 @@ technically a bug to produce a repository like this) wouldn't clone
 properly from the embedded Gerrit SSH or HTTP daemon.  Fixed upstream
 in JGit 0.7.0, but we never picked up the bug fix release.
 
+* Allow LDAP to unset the user name
++
+If the user name is configured to be set only by the LDAP directory,
+and an account has a user name, but the name is no longer present
+in the directory, Gerrit crashed during sign-in while trying to
+clear out the user name.  Fixed.
+
 Documentation Corrections
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/ChangeUserName.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/ChangeUserName.java
index d8951bf1e2..1509299447 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/ChangeUserName.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/ChangeUserName.java
@@ -36,6 +36,8 @@ import java.util.Collections;
 import java.util.concurrent.Callable;
 import java.util.regex.Pattern;
 
+import javax.annotation.Nullable;
+
 /** Operation to change the username of an account. */
 public class ChangeUserName implements Callable<VoidResult> {
   private static final Pattern USER_NAME_PATTERN =
@@ -77,7 +79,7 @@ public class ChangeUserName implements Callable<VoidResult> {
       final SshKeyCache sshKeyCache,
 
       @Assisted final ReviewDb db, @Assisted final IdentifiedUser user,
-      @Assisted final String newUsername) {
+      @Nullable @Assisted final String newUsername) {
     this.accountCache = accountCache;
     this.sshKeyCache = sshKeyCache;