From 4344df336b0e8839e71c809b37d0a73bd1d7c2f5 Mon Sep 17 00:00:00 2001
From: Ryan Cramer <ryan@processwire.com>
Date: Fri, 24 Dec 2021 10:49:22 -0500
Subject: [PATCH] Fix issue processwire/processwire-issues#1490

---
 wire/core/PagesLoader.php | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/wire/core/PagesLoader.php b/wire/core/PagesLoader.php
index b79183fe..f52a4ca9 100644
--- a/wire/core/PagesLoader.php
+++ b/wire/core/PagesLoader.php
@@ -662,7 +662,11 @@ class PagesLoader extends Wire {
 
 			foreach($row as $key => $value) {
 				if(strpos($key, '__')) {
-					$page->setFieldValue($key, $value, false);
+					if($value === null) {
+						$row[$key] = 'null'; // ensure detected by later isset in foreach($joinFields)
+					} else {
+						$page->setFieldValue($key, $value, false);
+					}
 				} else {
 					$page->setForced($key, $value);
 				}