Github user dbtsai commented on a diff in the pull request:
https://github.com/apache/spark/pull/21850#discussion_r204953202
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -414,6 +414,16 @@ object SimplifyConditionals extends Rule[LogicalPlan]
with PredicateHelper {
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
CaseWhen( h :+ t.head, None)
+
+ case CaseWhen(branches, elseValue) if branches.length == 1 =>
+ // Using pattern matching like `CaseWhen((cond, branchValue) ::
Nil, elseValue)` will not
+ // work since the implementation of `branches` can be
`ArrayBuffer`. A full test is in
--- End diff --
`sql("select case when a is null then 1 end col1 from t")` will create
`branches` with `ArrayBuffer` implementation.
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