transaction log not differentiating NULL values and empty string for char columns

The transaction log is not properly differentiating between NULL values and empty strings ("") for character columns

From the test case below:
We inserted a NULL and "" into the CHAR field, b. These are different values, but both are recorded as "" in the transaction_log output (shown in comments below in the test case

select * from t1;
+---+------+
| a | b |
+---+------+
| 1 | NULL |
| 2 | |
+---+------+
2 rows in set (0 sec)

test case: run with ./test-run --mysqld=--transaction_log_enable

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a INT NOT NULL, b CHAR(1000), PRIMARY KEY (a));
INSERT INTO t1 VALUES (1,NULL);

# Check the transaction_log contents:

SELECT PRINT_TRANSACTION_MESSAGE('transaction.log',(select max(entry_offset) from data_dictionary.transaction_log_transactions));

# Comments below are to show output, not part of the test case
# This gives us:
#| transaction_context {
# server_id: 1
# transaction_id: 60356
# start_timestamp: 1276642743948477
# end_timestamp: 1276642743991044
#}
#statement {
# type: INSERT
# start_timestamp: 1276642743948479
# end_timestamp: 1276642743991044
# insert_header {
# table_metadata {
# schema_name: "test"
# table_name: "t4"
# }
# field_metadata {
# type: INTEGER
# name: "a"
# }
# field_metadata {
# type: VARCHAR
# name: "b"
# }
# }
# insert_data {
# segment_id: 1
# end_segment: true
# record {
# insert_value: "1"
# insert_value: ""
# }
# }
#}
# |

INSERT INTO t4 VALUES (2,"");

SELECT PRINT_TRANSACTION_MESSAGE('transaction.log',(select max(entry_offset) from data_dictionary.transaction_log_transactions));
# Gives us:
#| transaction_context {
# server_id: 1
# transaction_id: 60358
# start_timestamp: 1276642757258085
# end_timestamp: 1276642757301771
#}
#statement {
# type: INSERT
# start_timestamp: 1276642757258087
# end_timestamp: 1276642757301770
# insert_header {
# table_metadata {
# schema_name: "test"
# table_name: "t1"
# }
# field_metadata {
# type: INTEGER
# name: "a"
# }
# field_metadata {
# type: VARCHAR
# name: "b"
# }
# }
# insert_data {
# segment_id: 1
# end_segment: true
# record {
# insert_value: "2"
# insert_value: ""
# }
# }
#}
# |