Fix for Gitaly nil encoding issue

lib/gitlab/gitaly_client.rb

@@ -233,6 +233,8 @@ module Gitlab
     end
     def self.encode(s)
+      return "" if s.nil?
+
       s.dup.force_encoding(Encoding::ASCII_8BIT)
     end

lib/gitlab/gitaly_client/commit_service.rb

@@ -274,7 +274,7 @@ module Gitlab
           repository: @gitaly_repo,
           left_commit_id: from_id,
           right_commit_id: to_id,
-          paths: options.fetch(:paths, []).map { |path| GitalyClient.encode(path) }
+          paths: options.fetch(:paths, []).compact.map { |path| GitalyClient.encode(path) }
         }
       end

spec/lib/gitlab/gitaly_client/commit_service_spec.rb

@@ -53,7 +53,7 @@ describe Gitlab::GitalyClient::CommitService do
     end
     it 'encodes paths correctly' do
-      expect { client.diff_from_parent(commit, paths: ['encoding/test.txt', 'encoding/テスト.txt']) }.not_to raise_error
+      expect { client.diff_from_parent(commit, paths: ['encoding/test.txt', 'encoding/テスト.txt', nil]) }.not_to raise_error
     end
   end

spec/lib/gitlab/gitaly_client_spec.rb

@@ -38,6 +38,20 @@ describe Gitlab::GitalyClient, skip_gitaly_mock: true do
     end
   end
+  describe 'encode' do
+    [
+      [nil, ""],
+      ["", ""],
+      ["  ", "  "],
+      %w(a1 a1),
+      ["编码", "\xE7\xBC\x96\xE7\xA0\x81".b]
+    ].each do |input, result|
+      it "encodes #{input.inspect} to #{result.inspect}" do
+        expect(described_class.encode(input)).to eq result
+      end
+    end
+  end
+
   describe 'allow_n_plus_1_calls' do
     context 'when RequestStore is enabled', :request_store do
       it 'returns the result of the allow_n_plus_1_calls block' do