Faulty nil checks after using a find method

[damianhxy]

In at least several controllers, .nil? checks are performed after calling .find( ... ). However, find throws an exception if an id is not found, so the checks are never reached.

They should be replaced with find_by where possible.

Some instances (found with grep -nr ".find(" -A 2)

course_user_data_controller.rb

    @editCUD = @course.course_user_data.find(params[:id])
    if @editCUD.nil?
      flash[:error] = "Can't find user in the course"
      redirect_to(action: "index") && return
    end

groups_controller.rb

    ass = @course.assessments.find(params[:ass])
    if !ass
      flash[:error] = "Assessment not found."
      redirect_to(action: :index) && return

users_controller.rb

    user = User.find(params[:id])
    if user.nil?
      flash[:error] = "Failed to edit user: user does not exist."
      redirect_to(users_path) && return
    end

lti_nrps_controller.rb

    lcd = LtiCourseDatum.find(params[:lcd_id])
    if lcd.nil? || lcd.membership_url.nil? || lcd.course_id.nil?
      raise LtiLaunchController::LtiError.new("Unable to update roster", :bad_request)
    end