generating nil id having id sequence defined, Why? - postgresql

Question

I have a table named async_data, which has id column also auto increment defined. But in production I am seeing some insert queries are failing saying
PG::NotNullViolation: ERROR: null value in column "id" violates not-null constraint
Rails Migration file
class CreateAsyncData < ActiveRecord::Migration[5.0]
def change
create_table :async_data do |t|
t.integer :request_id
t.integer :sourced_contact_id
t.integer :data_source_id
t.boolean :is_enriched
t.column :requested_params, :json
t.text :q
t.datetime :fetched_at
t.timestamps
end
end
end
CREATE TABLE public.async_data (
id integer NOT NULL,
request_id integer,
sourced_contact_id integer,
data_source_id integer,
is_enriched boolean DEFAULT false,
requested_params json,
fetched_at timestamp without time zone,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL,
q text,
is_processed boolean DEFAULT false NOT NULL,
is_data_pushed boolean DEFAULT false NOT NULL
);
\d async_data;
Table "public.async_data"
Column | Type | Collation | Nullable | Default
-------------------+-----------------------------+-----------+----------+----------------------------------------------------
id | integer | | not null | nextval('async_data_id_seq'::regclass)
request_id | integer | | |
source_company_id | integer | | |
data_source_id | integer | | |
is_enriched | boolean | | |
requested_params | json | | |
q | text | | |
fetched_at | timestamp without time zone | | |
created_at | timestamp without time zone | | not null |
updated_at | timestamp without time zone | | not null |
Indexes:
"async_data_pkey" PRIMARY KEY, btree (id)
--
-- Name: async_data_id_seq; Type: SEQUENCE; Schema: public; Owner: -
--
CREATE SEQUENCE public.async_data_id_seq
AS integer
START WITH 1
INCREMENT BY 1
NO MINVALUE
NO MAXVALUE
CACHE 1;
I want to re-produce the same in dev environment and want to know why id nil was generated.