diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index f1bfe697c4..f8febe712b 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -818,8 +818,10 @@ function template_preprocess_image(&$variables) {
   foreach (['width', 'height', 'alt', 'title', 'sizes'] as $key) {
     if (isset($variables[$key])) {
       // If the property has already been defined in the attributes, do not
-      // override, including NULL. Attributes can be an array or an object.
-      if ((is_array($variables['attributes']) && array_key_exists($key, $variables['attributes'])) || (is_object($variables['attributes']) && property_exists($variables['attributes'], $key))) {
+      // override, including NULL.
+      // @todo the cast to array below is needed to get tests pass on PHP 7.4,
+      // but requires a separate issue to fix.
+      if (array_key_exists($key, (array) $variables['attributes'])) {
         continue;
       }
       $variables['attributes'][$key] = $variables[$key];
diff --git a/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php b/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
index 85131ab8fa..5417dabc4a 100644
--- a/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
+++ b/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
@@ -183,7 +183,7 @@ public function prepareRow(Row $row) {
     $field_data = unserialize($row->getSourceProperty('field_data'));
     // @todo the use of the coalesce operator below is needed to get
     // migrate tests pass on PHP 7.4.
-    $row->setSourceProperty('field_settings', $field_data['settings']);
+    $row->setSourceProperty('field_settings', $field_data['settings'] ?? NULL);
 
     return parent::prepareRow($row);
   }
diff --git a/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
index d1807acad1..e8f15f6b9e 100644
--- a/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
+++ b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
@@ -72,7 +72,7 @@ public function prepareRow(Row $row) {
     $results = $query->execute()->fetchAssoc();
     // @todo the use of the coalesce operator below is needed to get
     // migrate tests pass on PHP 7.4.
-    $row->setSourceProperty($other_property . '_translated', $results['translation']);
+    $row->setSourceProperty($other_property . '_translated', $results['translation'] ?? NULL);
 
     parent::prepareRow($row);
   }