diff --git a/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/GBDT.java b/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/GBDT.java
index ec8276f..bc615fd 100644
--- a/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/GBDT.java
+++ b/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/GBDT.java
@@ -615,7 +615,12 @@ private List<List<?>> loadPandasCategorical(Section section){
 		String id = section.id();
 
 		try {
-			return PandasUtil.parsePandasCategorical(id);
+			List<List<?>> result = PandasUtil.parsePandasCategorical(id);
+			if(result == null){
+				result = Collections.emptyList();
+			}
+
+			return result;
 		} catch(Exception e){
 			throw new IllegalArgumentException(id, e);
 		}
diff --git a/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/PandasUtil.java b/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/PandasUtil.java
index 177705e..4cb9305 100644
--- a/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/PandasUtil.java
+++ b/pmml-lightgbm/src/main/java/org/jpmml/lightgbm/PandasUtil.java
@@ -19,7 +19,6 @@
 package org.jpmml.lightgbm;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import com.google.gson.Gson;
@@ -48,12 +47,7 @@ public List<List<?>> parsePandasCategorical(String string){
 		    .setObjectToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE)
 		    .create();
 
-		List<List<?>> result = gson.fromJson(element, ListOfLists.class);
-		if(result == null){
-			result = Collections.emptyList();
-		}
-
-		return result;
+		return gson.fromJson(element, ListOfLists.class);
 	}
 
 	static
diff --git a/pmml-lightgbm/src/test/java/org/jpmml/lightgbm/PandasUtilTest.java b/pmml-lightgbm/src/test/java/org/jpmml/lightgbm/PandasUtilTest.java
index ca48f5f..7317201 100644
--- a/pmml-lightgbm/src/test/java/org/jpmml/lightgbm/PandasUtilTest.java
+++ b/pmml-lightgbm/src/test/java/org/jpmml/lightgbm/PandasUtilTest.java
@@ -19,12 +19,12 @@
 package org.jpmml.lightgbm;
 
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 
 import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 public class PandasUtilTest {
 
@@ -32,7 +32,7 @@ public class PandasUtilTest {
 	public void parse() throws Exception {
 		List<List<?>> pandasCategories = parsePandasCategorical("null");
 
-		assertEquals(Collections.emptyList(), pandasCategories);
+		assertNull(pandasCategories);
 
 		pandasCategories = parsePandasCategorical("[[\"null\", \"A\", \"B, B\", \"C, [C], C\"], [-2, -1, 0, 1, 2], [-2.0, -1.0, 0.0, 1.0, 2.0], [false, true]]");