[SPARK-3448][SQL] Check for null in SpecificMutableRow.update

`SpecificMutableRow.update` doesn't check for null, and breaks existing `MutableRow` contract.

The tricky part here is that for performance considerations, the `update` method of all subclasses of `MutableValue` doesn't check for null and sets the null bit to false.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2325 from liancheng/check-for-null and squashes the following commits:

9366c44 [Cheng Lian] Check for null in SpecificMutableRow.update

1 files changed, 3 insertions, 1 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SpecificRow.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SpecificRow.scala
index 75ea0e8459..088f11ee4a 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SpecificRow.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SpecificRow.scala
@@ -227,7 +227,9 @@ final class SpecificMutableRow(val values: Array[MutableValue]) extends MutableR
     new SpecificMutableRow(newValues)
   }
 
-  override def update(ordinal: Int, value: Any): Unit = values(ordinal).update(value)
+  override def update(ordinal: Int, value: Any): Unit = {
+    if (value == null) setNullAt(ordinal) else values(ordinal).update(value)
+  }
 
   override def iterator: Iterator[Any] = values.map(_.boxed).iterator