new_contents: 
  """Make task_group_id nullable
  
  Revision ID: 1a4241cfd4cd
  Revises: 44047daa31a9
  Create Date: 2015-08-12 10:48:03.112117
  
  """
  
  from alembic import op
  import sqlalchemy as sa
  
  # revision identifiers, used by Alembic.
  revision = '1a4241cfd4cd'
  down_revision = '44047daa31a9'
  
  
  def upgrade():
    op.alter_column(
        "cycle_task_groups",
        "task_group_id",
        existing_type=sa.Integer(),
        nullable=True
    )
  
  
  def downgrade():
    op.alter_column(
        "cycle_task_groups",
        "task_group_id",
        existing_type=sa.Integer(),
        nullable=False
    )
  
subject: Make task_group_id nullable