diff --git a/sql/api/src/main/scala/org/apache/spark/sql/types/Metadata.scala b/sql/api/src/main/scala/org/apache/spark/sql/types/Metadata.scala
index 4c86bfba3a18d..f2cfcb984594d 100644
--- a/sql/api/src/main/scala/org/apache/spark/sql/types/Metadata.scala
+++ b/sql/api/src/main/scala/org/apache/spark/sql/types/Metadata.scala
@@ -40,13 +40,15 @@ import org.apache.spark.util.ArrayImplicits._
  * @since 1.3.0
  */
 @Stable
-sealed class Metadata private[types] (
-    private[types] val map: Map[String, Any],
-    @transient private[types] val runtimeMap: Map[String, Any])
+@SerialVersionUID(-3987058932362209243L)
+sealed class Metadata private[types] (private[types] val map: Map[String, Any])
     extends Serializable {
 
+  @transient private[types] var runtimeMap: Map[String, Any] = _
+  private[types] def setRuntimeMap(map: Map[String, Any]): Unit = runtimeMap = map
+
   /** No-arg constructor for kryo. */
-  protected def this() = this(null, null)
+  protected def this() = this(null)
 
   /** Tests whether this Metadata contains a binding for a key. */
   def contains(key: String): Boolean = map.contains(key)
@@ -137,7 +139,7 @@ sealed class Metadata private[types] (
 @Stable
 object Metadata {
 
-  private[this] val _empty = new Metadata(Map.empty, Map.empty)
+  private[this] val _empty = new Metadata(Map.empty)
 
   /** Returns an empty Metadata. */
   def empty: Metadata = _empty
@@ -309,7 +311,11 @@ class MetadataBuilder {
       // Save some memory when the metadata is empty
       Metadata.empty
     } else {
-      new Metadata(map.toMap, runtimeMap.toMap)
+      val metadata = new Metadata(map.toMap)
+      if (runtimeMap.nonEmpty) {
+        metadata.setRuntimeMap(runtimeMap.toMap)
+      }
+      metadata
     }
   }