code: def downgrade():
      with op.batch_alter_table("serialized_dag") as batch_op:
          batch_op.alter_column(
              "data", existing_type=sa.JSON, nullable=False
          )
          batch_op.drop_column("data_compressed")
  
imports: from __future__ import annotations
  import sqlalchemy
  from alembic import op
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types