Incorrect Nullable value in timestamp column

[GuptaManan100]

Overview of the Issue

Consider the following SQL statement

CREATE TABLE foo(
    id int primary key,
    a  varchar(255) null,
    b  varchar(255) null default 'foo',
    c  timestamp    null default current_timestamp()
);

Running this on vitess creates the table but the column c is not nullable. This is verified by running the following SQL statement

SELECT column_name              column_name,
       data_type                data_type,
       column_type              full_data_type,
       column_default           column_default,
       is_nullable              is_nullable
FROM information_schema.columns
WHERE table_name = 'foo'
ORDER BY ordinal_position;

Vitess results show that the column is not nullable but running the same queries on MySQL results in a nullable column

Reproduction Steps

Steps to reproduce this issue, example:

1. Run the vttestserver image and run the above queries to see the issue.