Address review comments

- Remove redundant .filter(_.nonEmpty) guard in PushDownUtils
- Fix misleading comment in InMemoryPartitionPredicateDeleteTable
- Add logDebug for each delete optimization outcome path

Author: szehon-ho

sql/catalyst/src/test/scala/org/apache/spark/sql/connector/catalog/InMemoryPartitionPredicateDeleteTable.scala

@@ -84,7 +84,7 @@ class InMemoryPartitionPredicateDeleteTable(
       candidateKeys
     }
 
-    // Handle data predicates (simulate data source with data column statistics)
+    // Handle data predicates (simulate a data source handling data filters with data statistics)
     if (dataStdPreds.isEmpty) {
       dataMap --= keysToProcess
     } else {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/OptimizeMetadataOnlyDeleteFromTable.scala

@@ -45,10 +45,15 @@ object OptimizeMetadataOnlyDeleteFromTable extends Rule[LogicalPlan] with Predic
           val normalizedPredicates = DataSourceStrategy.normalizeExprs(predicates, relation.output)
           val filtersOpt = tryTranslateToV2(normalizedPredicates)
           if (filtersOpt.exists(table.canDeleteWhere)) {
+            logDebug(s"Switching to delete with filters: " +
+              s"${filtersOpt.get.mkString("[", ", ", "]")}")
             DeleteFromTableWithFilters(relation, filtersOpt.get.toImmutableArraySeq)
           } else {
             tryDeleteWithPartitionPredicates(table, relation, normalizedPredicates)
-              .getOrElse(rowLevelPlan)
+              .getOrElse {
+                logDebug(s"Falling back to row-level delete on ${relation.table.name()}")
+                rowLevelPlan
+              }
           }
 
         case _: TruncatableTable if cond == TrueLiteral =>
@@ -93,6 +98,8 @@ object OptimizeMetadataOnlyDeleteFromTable extends Rule[LogicalPlan] with Predic
       combined = partPredicates.toArray ++ dataV2Filters
       if table.canDeleteWhere(combined)
     } yield {
+      logDebug(s"Switching to delete with PartitionPredicate filters: " +
+        s"${combined.mkString("[", ", ", "]")}")
       DeleteFromTableWithFilters(relation, combined.toImmutableArraySeq)
     }
   }

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/PushDownUtils.scala

@@ -149,7 +149,7 @@ object PushDownUtils extends Logging {
         case _ => None
       }
       if (fields.length == transforms.length) {
-        Some(fields.toSeq).filter(_.nonEmpty)
+        Some(fields.toSeq)
       } else {
         None
       }