[SPARK-52130][FOLLOW-UP][ML][CONNECT] Refine error message when model.summary is evicted

### What changes were proposed in this pull request?

Refine error message when model.summary is evicted.

In Spark Connect ML handler, `model.summary.XXX` invocation has different code path than `model.evaluate`, and it should raise readable error message when model.summary is evicted, otherwise the MLHandler will raise NullPointerException which is not friendly to end-users.

### Why are the changes needed?

Refine error message.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Manually.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #51048 from WeichenXu123/improve-scml-summary-error.

Authored-by: Weichen Xu <weichen.xu@databricks.com>
Signed-off-by: Weichen Xu <weichen.xu@databricks.com>

Author: WeichenXu123

sql/connect/server/src/main/scala/org/apache/spark/sql/connect/ml/MLHandler.scala

@@ -28,7 +28,7 @@ import org.apache.spark.ml.{Estimator, EstimatorUtils, Model, Transformer}
 import org.apache.spark.ml.evaluation.Evaluator
 import org.apache.spark.ml.param.{ParamMap, Params}
 import org.apache.spark.ml.tree.TreeConfig
-import org.apache.spark.ml.util.{MLWritable, Summary}
+import org.apache.spark.ml.util.{HasTrainingSummary, MLWritable, Summary}
 import org.apache.spark.sql.DataFrame
 import org.apache.spark.sql.connect.common.LiteralValueProtoConverter
 import org.apache.spark.sql.connect.ml.Serializer.deserializeMethodArguments
@@ -223,10 +223,17 @@ private[connect] object MLHandler extends Logging {
           .build()
 
       case proto.MlCommand.CommandCase.FETCH =>
-        val helper = AttributeHelper(
-          sessionHolder,
-          mlCommand.getFetch.getObjRef.getId,
-          mlCommand.getFetch.getMethodsList.asScala.toArray)
+        val objRefId = mlCommand.getFetch.getObjRef.getId
+        val methods = mlCommand.getFetch.getMethodsList.asScala.toArray
+        val obj = sessionHolder.mlCache.get(objRefId)
+        if (obj != null && obj.isInstanceOf[HasTrainingSummary[_]]
+          && methods(0).getMethod == "summary"
+          && !obj.asInstanceOf[HasTrainingSummary[_]].hasSummary) {
+          throw MLCacheInvalidException(
+            objRefId,
+            sessionHolder.mlCache.getOffloadingTimeoutMinute)
+        }
+        val helper = AttributeHelper(sessionHolder, objRefId, methods)
         val attrResult = helper.getAttribute
         attrResult match {
           case s: Summary =>