Allow deselecting a Workflow

app/controllers/collections/workflows_controller.rb

@@ -10,6 +10,7 @@ class Collections::WorkflowsController < ApplicationController
 
   private
     def set_workflow
-      @workflow = Workflow.find(params[:collection][:workflow_id])
+      workflow_id = params[:collection][:workflow_id]
+      @workflow = workflow_id.present? ? Workflow.find(workflow_id) : nil
     end
 end

app/views/collections/edit/_workflows.html.erb

@@ -4,8 +4,8 @@
   <div class="flex flex-wrap gap justify-center">
     <% Workflow.all.each do |workflow| %>
       <div class="workflow-preview txt-align-start border border-radius <%= 'workflow-preview--selected' if workflow == collection.workflow %>">
-        <%= button_to collection_workflow_path(collection), method: :patch do %>
-          <%= hidden_field_tag "collection[workflow_id]", workflow.id %>
+        <%= button_to collection_workflow_path(collection), method: :patch, aria: { label: workflow == collection.workflow ? "Stop using this workflow" : "Use this workflow" } do %>
+          <%= hidden_field_tag "collection[workflow_id]", workflow == collection.workflow ? "" : workflow.id %>
           <strong class="txt-small overflow-ellipsis flex-item-no-shrink"><%= workflow.name %></strong>
           <ul class="list-style-none txt-xx-small margin-none flex flex-column gap-half">
             <% workflow.stages.each do |stage| %>