old_contents: """allow nulls for run_id
  
  Revision ID: a8c4a736bde6
  Revises: 84291f40a231
  Create Date: 2020-12-02 12:14:35.220815
  
  """
  from alembic import op
  import sqlalchemy as sa
  from mlflow.store.model_registry.dbmodels.models import SqlModelVersion
  
  
  # revision identifiers, used by Alembic.
  revision = "a8c4a736bde6"
  down_revision = "84291f40a231"
  branch_labels = None
  depends_on = None
  
  
  def upgrade():
      with op.batch_alter_table(SqlModelVersion.__tablename__) as batch_op:
          batch_op.alter_column("run_id", nullable=True)
  
  
  def downgrade():
      pass
  
new_contents: """allow nulls for run_id
  
  Revision ID: a8c4a736bde6
  Revises: 84291f40a231
  Create Date: 2020-12-02 12:14:35.220815
  
  """
  from alembic import op
  import sqlalchemy as sa
  from mlflow.store.model_registry.dbmodels.models import SqlModelVersion
  
  
  # revision identifiers, used by Alembic.
  revision = "a8c4a736bde6"
  down_revision = "84291f40a231"
  branch_labels = None
  depends_on = None
  
  
  def upgrade():
      with op.batch_alter_table(SqlModelVersion.__tablename__) as batch_op:
          batch_op.alter_column("run_id", nullable=True, existing_type=sa.VARCHAR(32))
  
  
  def downgrade():
      pass
  
subject: Add existing type to alter_column in allows_null_for_run_id alembic migration (#3836)