Allow to delete tag release note

app/controllers/projects/releases_controller.rb

@@ -10,7 +10,14 @@ class Projects::ReleasesController < Projects::ApplicationController
   end
 
   def update
+    # Release belongs to Tag which is not active record object,
+    # it exists only to save a description to each Tag.
+    # If description is empty we should destroy the existing record.
+    if release_params[:description].present?
       release.update_attributes(release_params)
+    else
+      release.destroy
+    end
 
     redirect_to namespace_project_tag_path(@project.namespace, @project, @tag.name)
   end

changelogs/unreleased/issue_13270.yml

+---
+title: Allow to delete tag release note
+merge_request: 
+author: 

spec/controllers/projects/releases_controller_spec.rb

+require 'spec_helper'
+
+describe Projects::ReleasesController do
+  let!(:project) { create(:project) }
+  let!(:user)    { create(:user) }
+  let!(:release) { create(:release, project: project) }
+  let!(:tag)     { release.tag }
+
+  before do
+    project.team << [user, :developer]
+    sign_in(user)
+  end
+
+  describe 'GET #edit' do
+    it 'initializes a new release' do
+      tag_id = release.tag
+      project.releases.destroy_all
+
+      get :edit, namespace_id: project.namespace.path, project_id: project.path, tag_id: tag_id
+
+      release = assigns(:release)
+      expect(release).not_to be_nil
+      expect(release).not_to be_persisted
+    end
+
+    it 'retrieves an existing release' do
+      get :edit, namespace_id: project.namespace.path, project_id: project.path, tag_id: release.tag
+
+      release = assigns(:release)
+      expect(release).not_to be_nil
+      expect(release).to be_persisted
+    end
+  end
+
+  describe 'PUT #update' do
+    it 'updates release note description' do
+      update_release('description updated')
+
+      release = project.releases.find_by_tag(tag)
+      expect(release.description).to eq("description updated")
+    end
+
+    it 'deletes release note when description is null' do
+      expect { update_release('') }.to change(project.releases, :count).by(-1)
+    end
+  end
+
+  def update_release(description)
+    put :update,
+      namespace_id: project.namespace.to_param,
+      project_id: project.to_param,
+      tag_id: release.tag,
+      release: { description: description }
+  end
+end