import json

data = {}
for key in ['template_id', 'customer_id', 'code', 'source', 'remark', 'valid_from', 'valid_to']:
    val = params_kw.get(key, None) if hasattr(params_kw, 'get') else None
    if val is not None:
        data[key] = val

result = await create_voucher_instance(data)
return json.dumps(result)