serverless/lib/plugins/aws/lib/get-update-stack-params.js

export default {
  getUpdateStackParams(options) {
    const params = this.getSharedStackActionParams(options)

    // Policy must have at least one statement, otherwise no updates would be possible at all
    if (
      this.serverless.service.provider.stackPolicy &&
      Object.keys(this.serverless.service.provider.stackPolicy).length
    ) {
      params.StackPolicyBody = JSON.stringify({
        Statement: this.serverless.service.provider.stackPolicy,
      })
    }

    if (this.serverless.service.provider.rollbackConfiguration) {
      params.RollbackConfiguration =
        this.serverless.service.provider.rollbackConfiguration
    }

    if (this.serverless.service.provider.disableRollback) {
      params.DisableRollback = this.serverless.service.provider.disableRollback
    }
    return params
  },
}