Return an Empty Active Record Collection

You can use .none in a scope to short circuit the query in the event you don't have all the data.

Imagine this query but the project_type on a Project is nil

class User

  scope :active -> { where(archived: nil }

  scope :by_project, -> (project) do
    return none unless project.type.present?
    where(project_guid: project.guid, role: project.type)
  end

end

Just return none.

The cool thing about this is it's chainable. So you can still do something like:

project = Project.new(project_type: nil)

User.by_project(project).active