Ruby error receiving incoming email

production.log shows:

Email can not be processed: undefined method `find' for nil:NilClass

Return-Path: <REDACTED>^M
X-Original-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox^M
Delivered-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox^M
Received: from gitlab.vbox (unknown [10.10.0.3])^M
        by gitlab.vbox (Postfix) with ESMTP id 61F10110D4DA^M
        for <gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox>; Tue, 28 Mar 2017 12:18:41 -0400 (EDT)^M
Subject: Fibblez^M
^M
Sounds good!^M

If I send an email from the root user on the GitLab server itself, using telnet localhost 25, it works fine. The only difference is in the Received header. Below are two emails from the Maildir directory in my incoming Gitlab email user. One is the email that failed above, and another is one that succeeded. The succeeded one is first:

Return-Path: <root@gitlab.vbox>
X-Original-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox
Delivered-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox
Received: by gitlab.vbox (Postfix, from userid 0)
        id 2FA51110D4DA; Tue, 28 Mar 2017 12:16:38 -0400 (EDT)
Date: Tue, 28 Mar 2017 12:16:38 -0400
To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox
Subject: Bloop
User-Agent: Heirloom mailx 12.5 7/5/10
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Message-Id: <20170328161638.2FA51110D4DA@gitlab.vbox>
From: root@gitlab.vbox (root) 

haha

And the failed one (sent via telnet):

Return-Path:
X-Original-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox
Delivered-To: gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox
Received: from gitlab.vbox (unknown [10.10.0.3])
by gitlab.vbox (Postfix) with ESMTP id 61F10110D4DA
for gitlab-incoming+1b93876ec833d2a29e71f8c62a204449@gitlab.vbox; Tue, 28 Mar 2017 12:18:41 -0400 (EDT)
Subject: Fibblez

Sounds good!