From af25c7a505438e70a991da9c0f7ea042de5720e9 Mon Sep 17 00:00:00 2001
From: Adam Wood <72983627+webmaster-cses-org-uk@users.noreply.github.com>
Date: Sun, 7 Nov 2021 13:09:31 +0000
Subject: [PATCH] Guard against passing empty values to
 CRM_Core_DAO::getFieldValue()

This change removes a potential "getFieldValue failed" error that can be thrown if an empty scalar value occurs in a multiple-contact reference custom field.

See https://lab.civicrm.org/dev/core/-/issues/2939

Replaces https://github.com/eileenmcnaughton/civicrm-core/pull/13/commits which was opened against the wrong repo.
---
 CRM/Core/BAO/CustomField.php | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/CRM/Core/BAO/CustomField.php b/CRM/Core/BAO/CustomField.php
index b7a92bae4c..984afff29a 100644
--- a/CRM/Core/BAO/CustomField.php
+++ b/CRM/Core/BAO/CustomField.php
@@ -1096,11 +1096,17 @@ class CRM_Core_BAO_CustomField extends CRM_Core_DAO_CustomField {
       case 'Radio':
       case 'CheckBox':
         if ($field['data_type'] == 'ContactReference' && (is_array($value) || is_numeric($value))) {
-          $displayNames = [];
-          foreach ((array) $value as $contactId) {
-            $displayNames[] = CRM_Core_DAO::getFieldValue('CRM_Contact_DAO_Contact', $contactId, 'display_name');
+          // Issue #2939 - guard against passing empty values to CRM_Core_DAO::getFieldValue(), which would throw an exception
+          if (empty($value)) {
+            $display = '';
+          }
+          else {
+            $displayNames = [];
+            foreach ((array) $value as $contactId) {
+              $displayNames[] = CRM_Core_DAO::getFieldValue('CRM_Contact_DAO_Contact', $contactId, 'display_name');
+            }
+            $display = implode(', ', $displayNames);
           }
-          $display = implode(', ', $displayNames);
         }
         elseif ($field['data_type'] == 'ContactReference') {
           $display = $value;
-- 
2.25.1