diff --git a/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/ComparingPair.java b/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/ComparingPair.java
index c2efebf9d5..2947a709c3 100644
--- a/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/ComparingPair.java
+++ b/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/ComparingPair.java
@@ -64,7 +64,7 @@ TransHistoryItem two()
     * @param newItem to be added/removed item
     * @return a new object of this class
     */
-   public ComparingPair addOrRemove(TransHistoryItem newItem)
+   public ComparingPair tryAddOrRemoveIfExists(TransHistoryItem newItem)
    {
       if (isEmpty())
       {
diff --git a/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/TranslationHistoryPresenter.java b/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/TranslationHistoryPresenter.java
index c79873b826..0ac1de60df 100644
--- a/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/TranslationHistoryPresenter.java
+++ b/zanata-war/src/main/java/org/zanata/webtrans/client/presenter/TranslationHistoryPresenter.java
@@ -7,7 +7,6 @@
 import net.customware.gwt.presenter.client.EventBus;
 import net.customware.gwt.presenter.client.widget.WidgetPresenter;
 
-import org.zanata.common.ContentState;
 import org.zanata.webtrans.client.events.CopyDataToEditorEvent;
 import org.zanata.webtrans.client.events.NotificationEvent;
 import org.zanata.webtrans.client.events.ReviewCommentEvent;
@@ -30,7 +29,6 @@
 import com.google.common.base.Objects;
 import com.google.common.collect.Lists;
 import com.google.gwt.user.client.rpc.AsyncCallback;
-import com.google.gwt.view.client.SelectionChangeEvent;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 
@@ -143,7 +141,7 @@ public void copyIntoEditor(List<String> contents)
    @Override
    public void compareClicked(TransHistoryItem item)
    {
-      comparingPair = comparingPair.addOrRemove(item);
+      comparingPair = comparingPair.tryAddOrRemoveIfExists(item);
       if (comparingPair.isFull())
       {
          display.showDiff(comparingPair.one(), comparingPair.two(), messages.translationHistoryComparison(
diff --git a/zanata-war/src/test/java/org/zanata/webtrans/client/presenter/ComparingPairTest.java b/zanata-war/src/test/java/org/zanata/webtrans/client/presenter/ComparingPairTest.java
index e4b717f375..9185202b78 100644
--- a/zanata-war/src/test/java/org/zanata/webtrans/client/presenter/ComparingPairTest.java
+++ b/zanata-war/src/test/java/org/zanata/webtrans/client/presenter/ComparingPairTest.java
@@ -55,7 +55,7 @@ private static TransHistoryItem newItem(String versionNum)
    public void testAddWhenItsEmpty() throws Exception
    {
       TransHistoryItem newItem = newItem("1");
-      pair = ComparingPair.empty().addOrRemove(newItem);
+      pair = ComparingPair.empty().tryAddOrRemoveIfExists(newItem);
 
       assertThat(pair.one(), Matchers.sameInstance(newItem));
       assertThat(pair.two(), Matchers.nullValue());
@@ -65,7 +65,7 @@ public void testAddWhenItsEmpty() throws Exception
    public void addSameItemTwiceWillRemoveIt()
    {
       TransHistoryItem newItem = newItem("1");
-      pair = ComparingPair.empty().addOrRemove(newItem).addOrRemove(newItem);
+      pair = ComparingPair.empty().tryAddOrRemoveIfExists(newItem).tryAddOrRemoveIfExists(newItem);
 
       assertThat(pair.one(), Matchers.nullValue());
       assertThat(pair.two(), Matchers.nullValue());
@@ -77,13 +77,13 @@ public void addSameItemToFullPairWillBeIgnored() throws Exception
       TransHistoryItem one = newItem("1");
       TransHistoryItem two = newItem("2");
       TransHistoryItem three = newItem("3");
-      pair = ComparingPair.empty().addOrRemove(one).addOrRemove(two);
+      pair = ComparingPair.empty().tryAddOrRemoveIfExists(one).tryAddOrRemoveIfExists(two);
 
       assertThat(pair.isFull(), Matchers.is(true));
       assertThat(pair.one(), Matchers.sameInstance(one));
       assertThat(pair.two(), Matchers.sameInstance(two));
 
-      pair = pair.addOrRemove(three);
+      pair = pair.tryAddOrRemoveIfExists(three);
 
       assertThat(pair.isFull(), Matchers.is(true));
       assertThat(pair.one(), Matchers.sameInstance(one));
@@ -95,7 +95,7 @@ public void testContains() throws Exception
    {
       TransHistoryItem one = newItem("1");
       TransHistoryItem two = newItem("2");
-      pair = ComparingPair.empty().addOrRemove(one);
+      pair = ComparingPair.empty().tryAddOrRemoveIfExists(one);
 
       assertThat(pair.contains(one), Matchers.is(true));
       assertThat(pair.contains(two), Matchers.is(false));