Fatal error: Call to a member function getValue() on a non-object in /calendar/src/Plugin/views/row/Calendar.php

Problem/Motivation

When visiting the /events/month URI on the attached view I am getting:

Fatal error: Call to a member function getValue() on a non-object in /calendar/src/Plugin/views/row/Calendar.php on line 419

This comes from !empty($field->getValue()), where it should check the !empty($field)

Proposed resolution

As above, change to !empty($field) or perhaps:

if (!empty($field) && $date_str = $field->getValue()[0]['value']) {
// ...
          $item_start_date->setTimestamp($date_str);
// ...
        }

Remaining tasks

Review patch

User interface changes

N/A

API changes

N/A

Data model changes

N/A