Description

Undefined property notice.

Steps to reproduce

• Add a file property
• Load and select a file (an mp4 video in my case, don't know if it matters)
• Save

Page should now show a notice mentioning "undefined property on line 187" (in 3.1.18, line 185 on master) because, for a reason I didn't check, file isn't set.

What versions of softwares are you using?

• Papi: 3.1.18
• WordPress: 4.7.2