diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/TagSet.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/TagSet.java
index 5adfbd1c89..ba638474e3 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/git/TagSet.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/TagSet.java
@@ -348,6 +348,8 @@ class TagSet {
   }
 
   private static final class CachedRef extends AtomicReference<ObjectId> {
+    private static final long serialVersionUID = 1L;
+
     final int flag;
 
     CachedRef(Ref ref, int flag) {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/project/PermissionCollection.java b/gerrit-server/src/main/java/com/google/gerrit/server/project/PermissionCollection.java
index ca3bb4d2f2..932160ac26 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/project/PermissionCollection.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/project/PermissionCollection.java
@@ -127,17 +127,15 @@ public class PermissionCollection {
         }
       }
 
-      return new PermissionCollection(ref, permissions, perUser ? username : null);
+      return new PermissionCollection(permissions, perUser ? username : null);
     }
   }
 
-  private final String ref;
   private final Map<String, List<PermissionRule>> rules;
   private final String username;
 
-  private PermissionCollection(String ref,
-      Map<String, List<PermissionRule>> rules, String username) {
-    this.ref = ref;
+  private PermissionCollection(Map<String, List<PermissionRule>> rules,
+      String username) {
     this.rules = rules;
     this.username = username;
   }
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/workflow/CategoryFunction.java b/gerrit-server/src/main/java/com/google/gerrit/server/workflow/CategoryFunction.java
index 7b8b4b9590..e475b135d4 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/workflow/CategoryFunction.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/workflow/CategoryFunction.java
@@ -15,11 +15,8 @@
 package com.google.gerrit.server.workflow;
 
 import com.google.gerrit.common.data.ApprovalType;
-import com.google.gerrit.common.data.Permission;
 import com.google.gerrit.reviewdb.ApprovalCategory;
 import com.google.gerrit.reviewdb.PatchSetApproval;
-import com.google.gerrit.server.CurrentUser;
-
 import java.util.HashMap;
 import java.util.Map;
 
diff --git a/gerrit-server/src/main/java/gerrit/PRED_change_branch_1.java b/gerrit-server/src/main/java/gerrit/PRED_change_branch_1.java
index ee26c08902..59ec28b70c 100644
--- a/gerrit-server/src/main/java/gerrit/PRED_change_branch_1.java
+++ b/gerrit-server/src/main/java/gerrit/PRED_change_branch_1.java
@@ -16,7 +16,6 @@ package gerrit;
 
 import com.google.gerrit.reviewdb.Branch;
 import com.google.gerrit.reviewdb.Change;
-import com.google.gerrit.rules.PrologEnvironment;
 import com.google.gerrit.rules.StoredValues;
 
 import com.googlecode.prolog_cafe.lang.Operation;
@@ -39,7 +38,6 @@ public class PRED_change_branch_1 extends Predicate.P1 {
     engine.setB0();
     Term a1 = arg1.dereference();
 
-    PrologEnvironment env = (PrologEnvironment) engine.control;
     Change change = StoredValues.CHANGE.get(engine);
     Branch.NameKey name = change.getDest();
 
diff --git a/gerrit-server/src/main/java/gerrit/PRED_change_owner_1.java b/gerrit-server/src/main/java/gerrit/PRED_change_owner_1.java
index 20d70f3312..0be151ac1e 100644
--- a/gerrit-server/src/main/java/gerrit/PRED_change_owner_1.java
+++ b/gerrit-server/src/main/java/gerrit/PRED_change_owner_1.java
@@ -16,7 +16,6 @@ package gerrit;
 
 import com.google.gerrit.reviewdb.Account;
 import com.google.gerrit.reviewdb.Change;
-import com.google.gerrit.rules.PrologEnvironment;
 import com.google.gerrit.rules.StoredValues;
 
 import com.googlecode.prolog_cafe.lang.IntegerTerm;
@@ -42,7 +41,6 @@ public class PRED_change_owner_1 extends Predicate.P1 {
     engine.setB0();
     Term a1 = arg1.dereference();
 
-    PrologEnvironment env = (PrologEnvironment) engine.control;
     Change change = StoredValues.CHANGE.get(engine);
     Account.Id ownerId = change.getOwner();
 
diff --git a/gerrit-server/src/main/java/gerrit/PRED_change_project_1.java b/gerrit-server/src/main/java/gerrit/PRED_change_project_1.java
index c8d7e6df74..19f3e61a1a 100644
--- a/gerrit-server/src/main/java/gerrit/PRED_change_project_1.java
+++ b/gerrit-server/src/main/java/gerrit/PRED_change_project_1.java
@@ -16,7 +16,6 @@ package gerrit;
 
 import com.google.gerrit.reviewdb.Change;
 import com.google.gerrit.reviewdb.Project;
-import com.google.gerrit.rules.PrologEnvironment;
 import com.google.gerrit.rules.StoredValues;
 
 import com.googlecode.prolog_cafe.lang.Operation;
@@ -39,7 +38,6 @@ public class PRED_change_project_1 extends Predicate.P1 {
     engine.setB0();
     Term a1 = arg1.dereference();
 
-    PrologEnvironment env = (PrologEnvironment) engine.control;
     Change change = StoredValues.CHANGE.get(engine);
     Project.NameKey name = change.getProject();
 
diff --git a/gerrit-server/src/main/java/gerrit/PRED_change_topic_1.java b/gerrit-server/src/main/java/gerrit/PRED_change_topic_1.java
index 02786e52b5..a7694c1fb7 100644
--- a/gerrit-server/src/main/java/gerrit/PRED_change_topic_1.java
+++ b/gerrit-server/src/main/java/gerrit/PRED_change_topic_1.java
@@ -15,7 +15,6 @@
 package gerrit;
 
 import com.google.gerrit.reviewdb.Change;
-import com.google.gerrit.rules.PrologEnvironment;
 import com.google.gerrit.rules.StoredValues;
 
 import com.googlecode.prolog_cafe.lang.Operation;
@@ -38,7 +37,6 @@ public class PRED_change_topic_1 extends Predicate.P1 {
     engine.setB0();
     Term a1 = arg1.dereference();
 
-    PrologEnvironment env = (PrologEnvironment) engine.control;
     Term topicTerm = Prolog.Nil;
     Change change = StoredValues.CHANGE.get(engine);
     String topic = change.getTopic();
diff --git a/gerrit-server/src/main/java/gerrit/PRED_current_user_1.java b/gerrit-server/src/main/java/gerrit/PRED_current_user_1.java
index 335b4effad..516e87307c 100644
--- a/gerrit-server/src/main/java/gerrit/PRED_current_user_1.java
+++ b/gerrit-server/src/main/java/gerrit/PRED_current_user_1.java
@@ -15,7 +15,6 @@
 package gerrit;
 
 import com.google.gerrit.reviewdb.Account;
-import com.google.gerrit.rules.PrologEnvironment;
 import com.google.gerrit.rules.StoredValues;
 import com.google.gerrit.server.AnonymousUser;
 import com.google.gerrit.server.CurrentUser;
@@ -51,7 +50,6 @@ public class PRED_current_user_1 extends Predicate.P1 {
     engine.setB0();
     Term a1 = arg1.dereference();
 
-    PrologEnvironment env = (PrologEnvironment) engine.control;
     ChangeControl cControl = StoredValues.CHANGE_CONTROL.get(engine);
     CurrentUser curUser = cControl.getCurrentUser();
     Term resultTerm;