Return nil when fetching a wiki page with invalid arguments

Gitaly returns a GRPC::InvalidArgument response in certain cases, such
as empty titles or versions containing invalid characters.

On the Rails side we don't want to raise an error in this case, but
treat it the same as if a wiki page could not be found.

changelogs/unreleased/222699-wiki-find-page-empty-title.yml

+---
+title: Return nil when fetching a wiki page with invalid arguments
+merge_request: 44302
+author:
+type: fixed

lib/gitlab/git/wiki.rb

@@ -100,10 +100,6 @@ module Gitlab
         wrapped_gitaly_errors do
           gitaly_find_page(title: title, version: version, dir: dir)
         end
-      rescue Gitlab::Git::CommandError
-        # Return nil for invalid versions.
-        # This can be removed with https://gitlab.com/gitlab-org/gitaly/-/merge_requests/2323 in place.
-        nil
       end
 
       def file(name, version)
@@ -159,6 +155,8 @@ module Gitlab
         return unless wiki_page
 
         Gitlab::Git::WikiPage.new(wiki_page, version)
+      rescue GRPC::InvalidArgument
+        nil
       end
 
       def gitaly_find_file(name, version)

spec/lib/gitlab/git/wiki_spec.rb

@@ -51,6 +51,11 @@ RSpec.describe Gitlab::Git::Wiki do
       expect(subject.page(title: 'page1', dir: '').url_path).to eq 'page1'
       expect(subject.page(title: 'page1', dir: 'foo').url_path).to eq 'foo/page1'
     end
+
+    it 'returns nil for invalid arguments' do
+      expect(subject.page(title: '')).to be_nil
+      expect(subject.page(title: 'foo', version: ':')).to be_nil
+    end
   end
 
   describe '#delete_page' do

spec/support/shared_examples/models/wiki_shared_examples.rb

@@ -204,8 +204,9 @@ RSpec.shared_examples 'wiki model' do
       expect(page.title).to eq('index page')
     end
 
-    it 'returns nil if the page does not exist' do
-      expect(subject.find_page('non-existent')).to eq(nil)
+    it 'returns nil if the page or version does not exist' do
+      expect(subject.find_page('non-existent')).to be_nil
+      expect(subject.find_page('index page', 'non-existent')).to be_nil
     end
 
     it 'can find a page by slug' do