diff --git a/src/main/scala/com/databricks/spark/sql/perf/results.scala b/src/main/scala/com/databricks/spark/sql/perf/results.scala
index 209a732..87f0a28 100644
--- a/src/main/scala/com/databricks/spark/sql/perf/results.scala
+++ b/src/main/scala/com/databricks/spark/sql/perf/results.scala
@@ -148,9 +148,13 @@ class MLParams(
    * were defined (i.e., not equal to None) are included in the map.
    */
   def toMap: Map[String, String] = {
+    // Only outputs params that have values
     val allParams = ReflectionUtils.getConstructorArgs(this)
-    allParams.map { case (key: String, value: Any) =>
-      key -> value.toString
+    allParams.flatMap {
+      case (key: String, Some(value: Any)) =>
+        Some(key -> value.toString)
+      case _ =>
+        None
     }
   }
 
@@ -236,4 +240,4 @@ case class MLMetric(
 
 object MLMetric {
   val Invalid = MLMetric("Invalid", 0.0, false)
-}
\ No newline at end of file
+}