Creating an lb_event without location data causes a 500

Problem/Motivation

I was testing the module and I created a minimal event, without a value for field_location_reference or field_location_address. That caused:

Error: Call to a member function getValue() on null in ws_event_tokens() (line 77 of modules/contrib/ws_event/ws_event.tokens.inc).

Steps to reproduce

1. Create a lb_event node, filling in only the required fields.
2. Save

Proposed resolution

Make one of the fields required and/or make the token code gracefully handle missing values.

Remaining tasks

User interface changes

API changes

Data model changes