HyukjinKwon commented on a change in pull request #27991: [SPARK-31227][SQL] 
Non-nullable null type in complex types should not coerce to nullable type
URL: https://github.com/apache/spark/pull/27991#discussion_r397757665
 
 

 ##########
 File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
 ##########
 @@ -210,8 +206,15 @@ object Cast {
     case _ => false  // overflow
   }
 
+  /**
+   * Returns `true` iff it should change the nullability of this type in map 
type,
+   * array type, expressions such as cast, etc.
+   *
+   * Note that you should take the nullability context into account.
+   * For example, it should not force to nullable type when null type in array
+   * type is non-nullable which means an empty array of null type.
+   */
   def forceNullable(from: DataType, to: DataType): Boolean = (from, to) match {
-    case (NullType, _) => true
 
 Review comment:
   Hm .. okay

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