docs: function assertInstance(instance, model) {
    const modelName = get('modelName')(model)
    try {
      mongoose.model(modelName)
    } catch (err) {
      throw Error(`no such model as ${modelName}`)
    }
    const errMsg = stripIndents`
      Expected an instance of ${modelName} but got this:
      ${JSON.stringify(instance, undefined, 2)}`
    assert(instance instanceof model, errMsg)
  }