Migration from CSV: how to define a default value for autoincremental id field? I run migrations from CSV using Migrate Source CSV, Migrate Plus and Migrate Tools modules and it works fine.
The result of one of these migration is a custom entity which key is a 'id' field that has the 'AUTO_INCREMENT' property in the database.
Here is my migration_contractssubscriptions.yaml

id: migration_contractssubscriptions
migration_group: null
label: 'Contract Subscriptions migration from CSV'
source:
  plugin: csv
  path: /mypathto/migration_ContractsSubscriptions.csv
  delimiter: ';'
  enclosure: '"'
  header_row_count: 1
  keys:
    - id
process:
  id: id
  contract_id: contract_id
  member_id: member_id
  sharedwith_member_id: sharedwith_member_id
  comment: comment
  quantity01: quantity01
  quantity02: quantity02
  quantity03: quantity03
  quantity04: quantity04
  owner_id:
    plugin: default_value
    default_value: 1
destination:
  plugin: 'entity:contract_subscription'


I'd like to get rid of 'id' in my csv file and let the migration process handle the value of the resulting id.
I tried to remove keys: - id and id: id but I get an error...
How can I achieve that?
I finally understood that keys in source is the way to make each row of the csv file unique. It may be anything.
So I changed to:  

  keys:
    - contract_id
    - member_id


I removed id: idfrom processand it works!
The value of id field in the database is properly auto-incremented.