$params = ['id' => $this->_activityId];
CRM_Activity_BAO_Activity::retrieve($params, $defaults);
- $defaults['file_on_case_activity_subject'] = $defaults['subject'];
+ $defaults['file_on_case_activity_subject'] = $defaults['subject'] ?? '';
$defaults['file_on_case_target_contact_id'] = $defaults['target_contact'];
// If this contact has an open case, supply it as a default