MDEV-35122 Incorrect NULL value handling for instantly dropped BLOB columns

Problem:
=======
- Redundant table fails to insert into the table after
instant drop blob column. Instant drop column only marking
the column as hidden and consecutive insert statement tries
to insert NULL value for the dropped BLOB column and returns
the fixed length of the blob type as 65535. This lead to
row size too large error.

Fix:
====
 For redundant table, if the non-fixed dropped column can be null
then set the length of the field type as 0.

Author: Thirunarayanan

mysql-test/suite/innodb/r/instant_alter_bugs.result

@@ -529,4 +529,13 @@ c INT as (b) VIRTUAL)ENGINE=InnoDB CHARACTER SET utf32;
 ALTER TABLE t1 DROP COLUMN a;
 ALTER TABLE t1 DROP COLUMN c;
 DROP TABLE t1;
+#
+#  MDEV-35122  Incorrect NULL value handling for instantly
+#                 dropped BLOB columns
+#
+CREATE TABLE t1 (c1 INT, c2 BLOB, c3 BLOB NOT NULL) ROW_FORMAT=REDUNDANT,ENGINE=InnoDB;
+ALTER TABLE t1 DROP c2;
+ALTER TABLE t1 DROP c3;
+INSERT INTO t1 VALUES(1);
+DROP TABLE t1;
 # End of 10.5 tests

mysql-test/suite/innodb/t/instant_alter_bugs.test

@@ -565,4 +565,14 @@ ALTER TABLE t1 DROP COLUMN a;
 ALTER TABLE t1 DROP COLUMN c;
 DROP TABLE t1;
 
+--echo #
+--echo #  MDEV-35122  Incorrect NULL value handling for instantly
+--echo #                 dropped BLOB columns
+--echo #
+CREATE TABLE t1 (c1 INT, c2 BLOB, c3 BLOB NOT NULL) ROW_FORMAT=REDUNDANT,ENGINE=InnoDB;
+ALTER TABLE t1 DROP c2;
+ALTER TABLE t1 DROP c3;
+INSERT INTO t1 VALUES(1);
+DROP TABLE t1;
+
 --echo # End of 10.5 tests

storage/innobase/row/row0row.cc

@@ -250,6 +250,14 @@ row_build_index_entry_low(
 			dict_col_copy_type(f.col, &dfield->type);
 			if (f.col->is_nullable()) {
 				dfield_set_null(dfield);
+				if (f.col->mtype == DATA_BINARY
+				    && !dict_table_is_comp(index->table)) {
+					/* In case of redundant row format,
+					if the non-fixed dropped column
+					is null then set the length of the
+					field data type as 0 */
+					dfield->type.len= 0;
+				}
 			} else {
 				dfield_set_data(dfield, field_ref_zero,
 						f.fixed_len);