Exception when previewing document as iPad site

Steps to reproduce:
1) Log into Go Green Enterprise as admin/admin
2) Create a new document or open /content/documents/hippogogreen/events/2014/11/jfall
3) Save the document and View/IPad Magazine
Expected: Rendered page
Actual: black figure with caption 'We love to have captions on images'
Stacktrace in console:

[INFO] [talledLocalContainer] 03.12.2013 15:34:50 ERROR [freemarker.log.Log4JLoggerFactory$Log4JLogger.error():96] Template processing error: "Error on line 56, column 33 in jcr:/hst:hst/hst:configurations/ipadmag/hst:templates/events.detail.ftl\ndocument.firstImage is undefined.\nIt cannot be assigned to image"
[INFO] [talledLocalContainer]
[INFO] [talledLocalContainer] Error on line 56, column 33 in jcr:/hst:hst/hst:configurations/ipadmag/hst:templates/events.detail.ftl
[INFO] [talledLocalContainer] document.firstImage is undefined.
[INFO] [talledLocalContainer] It cannot be assigned to image
[INFO] [talledLocalContainer] The problematic instruction:
[INFO] [talledLocalContainer] ----------
[INFO] [talledLocalContainer] ==> assignment: image=document.firstImage [on line 56, column 33 in jcr:/hst:hst/hst:configurations/ipadmag/hst:templates/events.detail.ftl]
[INFO] [talledLocalContainer] ----------
[INFO] [talledLocalContainer]
[INFO] [talledLocalContainer] Java backtrace for programmers:
[INFO] [talledLocalContainer] ----------
[INFO] [talledLocalContainer] freemarker.core.InvalidReferenceException: Error on line 56, column 33 in jcr:/hst:hst/hst:configurations/ipadmag/hst:templates/events.detail.ftl
[INFO] [talledLocalContainer] document.firstImage is undefined.
[INFO] [talledLocalContainer] It cannot be assigned to image
[INFO] [talledLocalContainer] at freemarker.core.Assignment.accept(Assignment.java:111)