diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
index 6d94764f1bfacc256c0d29874deffa63c8369684..eed773d4cb36857aa3b179a6782a8d363ccdbfd5 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/objects/objects.scala
@@ -996,6 +996,8 @@ case class AssertNotNull(child: Expression, walkedTypePath: Seq[String] = Nil)
   override def foldable: Boolean = false
   override def nullable: Boolean = false
 
+  override def flatArguments: Iterator[Any] = Iterator(child)
+
   private val errMsg = "Null value appeared in non-nullable field:" +
     walkedTypePath.mkString("\n", "\n", "\n") +
     "If the schema is inferred from a Scala tuple/case class, or a Java bean, " +