Rails controller derived from `InheritedResources::Base` (see https://github.com/josevalim/inherited_resources) that plays nice with Devise (see http://devise.plataformatec.com.br/) when updating a user record that has no changes to password. Discussed on my blog at http://archlever.blogspot.com/2013/06/tools-save-you-time-except-when-they.html

users_controller.rb

# Actions for Users. Not necessarily a finer distinction one way or another yet.
class UsersController < InheritedResources::Base
  # FIXME respond_to :json # should spec JSON actions, too
  respond_to :html
  load_and_authorize_resource

  def update
    # Devise has the convention that, for updates where the password is NOT to
    # be modified, the password and password-confirmation fields MUST NOT be
    # submitted. inherited_resources, of course, just sees two text fields and
    # wraps them up along with the rest of the form. Oops.
    remove_password_parameters if password_fields_are_empty?
    super
  end

  private

  def password_fields_are_empty?
    params['user']['password'].empty? and
      params['user']['password_confirmation'].empty?
  end

  def remove_password_parameters
    params['user'].delete 'password'
    params['user'].delete 'password_confirmation'
  end

end