Allow wiki pages to be empty

In this commit we allow wiki pages to be empty (mostly removing
the validation in the backend).

This aligns the existing behavior because users can push
wiki empty pages through git and that will trigger an error
because of the existing validator.

Changelog: changed

app/models/wiki_page.rb

@@ -40,7 +40,6 @@ class WikiPage
   end
 
   validates :title, presence: true
-  validates :content, presence: true
   validate :validate_path_limits, if: :title_changed?
   validate :validate_content_size_limit, if: :content_changed?
 

spec/models/wiki_page_spec.rb

@@ -201,11 +201,10 @@ RSpec.describe WikiPage do
       expect(subject.errors.messages).to eq(title: ["can't be blank"])
     end
 
-    it "validates presence of content" do
+    it "does not validate presence of content" do
       subject.attributes.delete(:content)
 
-      expect(subject).not_to be_valid
-      expect(subject.errors.messages).to eq(content: ["can't be blank"])
+      expect(subject).to be_valid
     end
 
     describe '#validate_content_size_limit' do

spec/support/shared_examples/features/wiki/user_creates_wiki_page_shared_examples.rb

@@ -20,17 +20,6 @@ RSpec.shared_examples 'User creates wiki page' do
       click_link "Create your first page"
     end
 
-    it "shows validation error message if the form is force submitted", :js do
-      page.within(".wiki-form") do
-        fill_in(:wiki_content, with: "")
-
-        page.execute_script("document.querySelector('.wiki-form').submit()")
-        page.accept_alert # manually force form submit
-      end
-
-      expect(page).to have_content("The form contains the following error:").and have_content("Content can't be blank")
-    end
-
     it "disables the submit button", :js do
       page.within(".wiki-form") do
         fill_in(:wiki_content, with: "")

spec/support/shared_examples/features/wiki/user_updates_wiki_page_shared_examples.rb

@@ -90,19 +90,6 @@ RSpec.shared_examples 'User updates wiki page' do
       expect(page).to have_field('wiki[message]', with: 'Update Wiki title')
     end
 
-    it 'shows a validation error message if the form is force submitted', :js do
-      fill_in(:wiki_content, with: '')
-
-      page.execute_script("document.querySelector('.wiki-form').submit()")
-      page.accept_alert # manually force form submit
-
-      expect(page).to have_selector('.wiki-form')
-      expect(page).to have_content('Edit Page')
-      expect(page).to have_content('The form contains the following error:')
-      expect(page).to have_content("Content can't be blank")
-      expect(find('textarea#wiki_content').value).to eq('')
-    end
-
     it "disables the submit button", :js do
       page.within(".wiki-form") do
         fill_in(:wiki_content, with: "")