Identity column has null values

[rachit-prodigal]

I created a table in databricks using a dbt model pre hook 

CREATE TABLE IF NOT EXISTS accounts (
  account_id BIGINT GENERATED ALWAYS AS IDENTITY,
  description STRING
  other columns
)

I use the same dbt model to merge values into this table in the post-hook

post_hook = [
"
  MERGE INTO accounts AS target
  USING incremental_accounts AS source
  ON <join-condition>
  WHEN MATCHED THEN UPDATE SET
  target.description = source.description
  WHEN NOT MATCHED BY target THEN
  INSERT(description)
  VALUES (source.description)
"

the model code itself is simple in the file incremental_accounts.sql

SELECT description from new_accounts

The table accounts was created by this model and only updated by this model by the post-hook queries.

The problem is that I noticed null values in account_id which should not be the case as it is auto-generated. 

I identified the same issue with 4 other tables which were built similarly using dbt models.

Can you please help me with this issue.