code: def upgrade():
      """Apply Add description field to ``Variable`` model"""
      with op.batch_alter_table("variable", schema=None) as batch_op:
          batch_op.add_column(
              sa.Column("description", sa.Text(), nullable=True)
          )
  
imports: from __future__ import annotations
  import sqlalchemy
  from alembic import op
label_desc: Use image node_id 1 for calling a global function with example usage: upgrade() without return types