diff --git a/main/src/com/google/refine/ProjectManager.java b/main/src/com/google/refine/ProjectManager.java
index 89070ac29..2447ecd5e 100644
--- a/main/src/com/google/refine/ProjectManager.java
+++ b/main/src/com/google/refine/ProjectManager.java
@@ -68,7 +68,7 @@ import com.google.refine.util.ParsingUtilities;
  */
 public abstract class ProjectManager {
     // last n expressions used across all projects
-    static protected final int s_expressionHistoryMax = 100;
+    static public final int EXPRESSION_HISTORY_MAX = 100;
 
     // If a project has been idle this long, flush it from memory
     static protected final int PROJECT_FLUSH_DELAY = 1000 * 60 * 15; // 15 minutes
@@ -610,7 +610,7 @@ public abstract class ProjectManager {
     * @param ps
     */
    static protected void preparePreferenceStore(PreferenceStore ps) {
-       ps.put("scripting.expressions", new TopList(s_expressionHistoryMax));
+       ps.put("scripting.expressions", new TopList(EXPRESSION_HISTORY_MAX));
        ps.put("scripting.starred-expressions", new TopList(Integer.MAX_VALUE));
    }
 }
diff --git a/main/src/com/google/refine/commands/expr/LogExpressionCommand.java b/main/src/com/google/refine/commands/expr/LogExpressionCommand.java
index 71df8ca24..6ccad3a93 100644
--- a/main/src/com/google/refine/commands/expr/LogExpressionCommand.java
+++ b/main/src/com/google/refine/commands/expr/LogExpressionCommand.java
@@ -41,6 +41,7 @@ import javax.servlet.http.HttpServletResponse;
 
 import com.google.refine.ProjectManager;
 import com.google.refine.commands.Command;
+import com.google.refine.preference.PreferenceStore;
 import com.google.refine.preference.TopList;
 
 public class LogExpressionCommand extends Command {
@@ -55,9 +56,14 @@ public class LogExpressionCommand extends Command {
     	
         try {
             String expression = request.getParameter("expression");
-            
-            ((TopList) ProjectManager.singleton.getPreferenceStore().get("scripting.expressions"))
-                .add(expression);
+
+            PreferenceStore prefStore = ProjectManager.singleton.getPreferenceStore();
+            TopList topList = (TopList) prefStore.get("scripting.expressions");
+            if (topList == null) {
+            	topList = new TopList(ProjectManager.EXPRESSION_HISTORY_MAX);
+            	prefStore.put("scripting.expressions", topList);
+            }
+            topList.add(expression);
             
             response.setCharacterEncoding("UTF-8");
             response.setHeader("Content-Type", "application/json");
diff --git a/main/tests/server/src/com/google/refine/commands/expr/LogExpressionCommandTests.java b/main/tests/server/src/com/google/refine/commands/expr/LogExpressionCommandTests.java
index 1283820ef..9222a76e2 100644
--- a/main/tests/server/src/com/google/refine/commands/expr/LogExpressionCommandTests.java
+++ b/main/tests/server/src/com/google/refine/commands/expr/LogExpressionCommandTests.java
@@ -1,18 +1,33 @@
 package com.google.refine.commands.expr;
 
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.mock;
+import com.google.refine.ProjectManager;
+import com.google.refine.ProjectManagerStub;
+import com.google.refine.commands.Command;
 import com.google.refine.commands.CommandTestBase;
+import com.google.refine.preference.PreferenceStore;
+import com.google.refine.preference.TopList;
+
 import java.io.IOException;
+import java.util.Collections;
 
 import javax.servlet.ServletException;
 
+import org.testng.Assert;
 import org.testng.annotations.BeforeMethod;
 import org.testng.annotations.Test;
 
 public class LogExpressionCommandTests extends CommandTestBase {
 	
+	PreferenceStore prefStore;
+	
 	@BeforeMethod
 	public void setUpCommand() {
 		command = new LogExpressionCommand();
+		ProjectManager.singleton = mock(ProjectManager.class);
+		prefStore = new PreferenceStore();
+		when(ProjectManager.singleton.getPreferenceStore()).thenReturn(prefStore);
 	}
 	
 	@Test
@@ -20,4 +35,16 @@ public class LogExpressionCommandTests extends CommandTestBase {
 		command.doPost(request, response);
 		assertCSRFCheckFailed();
 	}
+	
+	@Test
+	public void testNullExpressions() throws ServletException, IOException {
+		prefStore.put("scripting.expressions", null);
+		when(request.getParameter("csrf_token")).thenReturn(Command.csrfFactory.getFreshToken());
+		when(request.getParameter("expression")).thenReturn("grel:value+'a'");
+		
+		command.doPost(request, response);
+		
+		TopList topList = (TopList)prefStore.get("scripting.expressions");
+		Assert.assertEquals(topList.getList(), Collections.singletonList("grel:value+'a'"));
+	}
 }