Should @id annotated columns be marked as not null?

I noticed that id columns are displayed as if it's nullable when deployed to dbdocs.

For example, this prisma schema produces such dbml modeling which lucks not null annotation for user_id column.

Input: schema.prisma

model User {
  user_id Int    @id
  name    String
}

Output: schema.dbml

Table User {
  user_id Int [pk]
  name String [not null]
}

I thought it's bit confusing, but is that somehow a designed behavior?

notiz-dev / prisma-dbml-generator