3 files changed, 16 insertions, 1 deletions
diff --git a/changelogs/unreleased/dont-blow-up-when-email-has-no-references-header.yml b/changelogs/unreleased/dont-blow-up-when-email-has-no-references-header.yml
new file mode 100644
index 00000000000..a4345b70744
--- /dev/null
+++ b/changelogs/unreleased/dont-blow-up-when-email-has-no-references-header.yml
@@ -0,0 +1,5 @@
+---
+title: Gracefully handle failures for incoming emails which do not match on the To
+  header, and have no References header
+merge_request:
+author:
diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index 419d56a51e0..c270c0ea9ff 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -70,6 +70,8 @@ module Gitlab
           # Handle emails from clients which append with commas,
           # example clients are Microsoft exchange and iOS app
           Gitlab::IncomingEmail.scan_fallback_references(references)
+        when nil
+          []
         end
       end
 
diff --git a/spec/lib/gitlab/email/receiver_spec.rb b/spec/lib/gitlab/email/receiver_spec.rb
index 2a86b427806..f127e45ae6a 100644
--- a/spec/lib/gitlab/email/receiver_spec.rb
+++ b/spec/lib/gitlab/email/receiver_spec.rb
@@ -7,9 +7,17 @@ describe Gitlab::Email::Receiver, lib: true do
   context "when we cannot find a capable handler" do
     let(:email_raw) { fixture_file('emails/valid_reply.eml').gsub(mail_key, "!!!") }
 
-    it "raises a UnknownIncomingEmail" do
+    it "raises an UnknownIncomingEmail error" do
       expect { receiver.execute }.to raise_error(Gitlab::Email::UnknownIncomingEmail)
     end
+
+    context "and the email contains no references header" do
+      let(:email_raw) { fixture_file("emails/auto_reply.eml").gsub(mail_key, "!!!") }
+
+      it "raises an UnknownIncomingEmail error" do
+        expect { receiver.execute }.to raise_error(Gitlab::Email::UnknownIncomingEmail)
+      end
+    end
   end
 
   context "when the email is blank" do