After exporting JIRA in printable view, base URL appears as 'undefined'

Summary  

After exporting JIRA issue in printable format, message mentioning "JIRA's base URL is set to undefined" appears

Steps to Reproduce

1. Open issue
2. Click Export > Printable
3. Printable format opens

Expected Results

The printable version of the issue is shown.

Actual Results

The printable version of the issue is shown and also the following message appears:
"JIRA's base URL is set to undefined but you are accessing JIRA from http://<server_name>"

Workaround

None

Notes

• This was tested on JIRA 7.5.1, but wasn't reproducible
• Base URL is set correctly and there are no base-URL related message in the logs
• The message appears while accessing JIRA both via proxy and directly via Tomcat port
• Bug also shows when using the LegacyEdit functionality
• The message is only shown to users with administration rights.