code: def downgrade():
      with op.batch_alter_table("dashboards") as batch_op:
          batch_op.alter_column(
              "position_json",
              existing_type=MediumText(),
              type_=sa.Text(),
              existing_nullable=True,
          )
  
imports: import sqlalchemy
  from alembic import op
  from superset.utils.core import MediumText
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types