Safety code when overriding entity fields

Problem/Motivation

Because of a content/config issue (I don't exactly know), we are in a situation where viewing a node is causing an exception while executing this module's code. Some safety code resolves it. (patch to follow)

Steps to reproduce

Unfortunately I don't understand our particular situation enough to describe how to recreate.

Proposed resolution

Add some harmless safety code.

Remaining tasks

Patch to be uploaded.

User interface changes

None.

API changes

None.

Data model changes

None.