Email notifications are showing "Failed to retrieve user" as the sender

Issue Summary

Email notifications are being delivered however, the sender is displayed as "Failed to retrieve user" in the "From" field.

Environment

Cloud

Steps to Reproduce

1. Generate an email notification event.

Expected Results

The sender is displayed as the user who created the change and triggered the notification event.

Actual Results

The sender is displayed as "Failed to retrieve user"

The below exception is thrown in the xxxxxxx.log file:

Sending email with Message-Id <JIRA.761671.1562017467000.<aaid>@Atlassian.JIRA>: To='"?"' Subject='xxxxxxx' From='null' 
FromName='"Failed to Retrieve User <aaid>" (JIRA)' EnvelopeFrom='null' Cc='null' Bcc='null' ReplyTo='null' InReplyTo='<JIRA.761671.1562017467000@Atlassian.JIRA>' MimeType='text/html' Encoding='UTF-8' Multipart='javax.mail.internet.MimeMultipart@28341720' MessageId='<JIRA.761671.1562017467000.<aaid>@Atlassian.JIRA>' ExcludeSubjectPrefix=false'

Notes

This is a graphical issues and the functionality is not impacted.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available