Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/15979#discussion_r89936859
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/encoders/ExpressionEncoder.scala
---
@@ -47,6 +47,14 @@ object ExpressionEncoder {
// We convert the not-serializable TypeTag into StructType and
ClassTag.
val mirror = typeTag[T].mirror
val tpe = typeTag[T].tpe
+
+ if (ScalaReflection.optionOfNonFlatType(tpe)) {
+ throw new UnsupportedOperationException(
+ "Cannot create encoder for Option of non-flat type, as non-flat
type is represented " +
+ "as a row, and the entire row can not be null in Spark SQL like
normal databases. " +
+ "You can wrap your type with Tuple1 if you do want top level
null objects.")
--- End diff --
Let's provide an example in the error message to help users understand how
to handle this case.
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