diff --git a/gluten-core/src/main/scala/org/apache/gluten/expression/AggregateFunctionsBuilder.scala b/gluten-core/src/main/scala/org/apache/gluten/expression/AggregateFunctionsBuilder.scala
index 6ac2c67eb0860..00b4818545f8e 100644
--- a/gluten-core/src/main/scala/org/apache/gluten/expression/AggregateFunctionsBuilder.scala
+++ b/gluten-core/src/main/scala/org/apache/gluten/expression/AggregateFunctionsBuilder.scala
@@ -31,7 +31,8 @@ object AggregateFunctionsBuilder {
     // First handle the custom aggregate functions
     val (substraitAggFuncName, inputTypes) =
       if (
-        ExpressionMappings.expressionExtensionTransformer.extensionExpressionsMapping.contains(
+        ExpressionMappings.expressionExtensionTransformer != null &&
+          ExpressionMappings.expressionExtensionTransformer.extensionExpressionsMapping.contains(
           aggregateFunc.getClass)
       ) {
         val (substraitAggFuncName, inputTypes) =
diff --git a/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionConverter.scala b/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionConverter.scala
index 3ca66b51897b0..fff914a45555a 100644
--- a/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionConverter.scala
+++ b/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionConverter.scala
@@ -155,8 +155,9 @@ object ExpressionConverter extends SQLConfHelper with Logging {
 
     expr match {
       case extendedExpr
-          if ExpressionMappings.expressionExtensionTransformer.extensionExpressionsMapping.contains(
-            extendedExpr.getClass) =>
+          if ExpressionMappings.expressionExtensionTransformer != null
+            && ExpressionMappings.expressionExtensionTransformer.extensionExpressionsMapping
+              .contains(extendedExpr.getClass) =>
         // Use extended expression transformer to replace custom expression first
         ExpressionMappings.expressionExtensionTransformer
           .replaceWithExtensionExpressionTransformer(substraitExprName, extendedExpr, attributeSeq)
diff --git a/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionMappings.scala b/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionMappings.scala
index e0628f11102d2..c07240efca7a7 100644
--- a/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionMappings.scala
+++ b/gluten-core/src/main/scala/org/apache/gluten/expression/ExpressionMappings.scala
@@ -338,8 +338,11 @@ object ExpressionMappings {
 
   def expressionsMap: Map[Class[_], String] = {
     val blacklist = GlutenConfig.getConf.expressionBlacklist
-    val supportedExprs = defaultExpressionsMap ++
-      expressionExtensionTransformer.extensionExpressionsMapping
+
+    var supportedExprs = defaultExpressionsMap
+    if (expressionExtensionTransformer != null) {
+      supportedExprs = supportedExprs ++ expressionExtensionTransformer.extensionExpressionsMapping
+    }
     if (blacklist.isEmpty) {
       supportedExprs
     } else {