code: def upgrade():
      bind = op.get_bind()
      session = db.Session(bind=bind)
  
      for model in (Query, SavedQuery):
          for record in session.query(model).filter(
              model.schema == "null"
          ):
              record.schema = None
  
          session.commit()
  
      session.close()
  
file_path: superset/superset/migrations/versions/2022-03-02_09-20_b5a422d8e252_fix_query_and_saved_query_null_schema.py
imports: from alembic import op
  from sqlalchemy import Column, Integer, String
  from sqlalchemy.ext.declarative import declarative_base
  from superset import db
label_desc: Use image node_id 1 for calling a global function with example usage: upgrade() without return types