Issue #2784783 by RytoEX, quietone, jofitz, Charlotte17, Anybody,...

Issue #2784783 by RytoEX, quietone, jofitz, Charlotte17, Anybody, tomhollevoet, catch, Grevil: Migration of nodes with cck nodereferrer fields fails (SQL error)

core/modules/node/src/Plugin/migrate/source/d6/Node.php

@@ -297,6 +297,10 @@ protected function getFieldData(array $field, Row $node) {
 
     if (isset($query)) {
       $columns = array_keys($field['db_columns']);
+      // If there are no columns then there are no values to return.
+      if (empty($columns)) {
+        return [];
+      }
 
       // Add every column in the field's schema.
       foreach ($columns as $column) {

core/modules/node/tests/src/Kernel/Plugin/migrate/source/d6/NodeTest.php

@@ -38,6 +38,18 @@ public function providerSource() {
         'active' => '1',
         'locked' => '0',
       ],
+      [
+        'field_name' => 'field_test_empty_db_columns',
+        'type' => 'empty_db_columns',
+        'global_settings' => 'a:0:{}',
+        'required' => '0',
+        'multiple' => '0',
+        'db_storage' => '1',
+        'module' => 'empty_db_columns',
+        'db_columns' => 'a:0:{}',
+        'active' => '1',
+        'locked' => '0',
+      ],
     ];
     $tests[0]['source_data']['content_node_field_instance'] = [
       [
@@ -52,6 +64,18 @@ public function providerSource() {
         'widget_module' => 'number',
         'widget_active' => '1',
       ],
+      [
+        'field_name' => 'field_test_empty_db_columns',
+        'type_name' => 'story',
+        'weight' => '33',
+        'label' => 'Empty db_columns Field',
+        'widget_type' => 'empty_db_columns',
+        'widget_settings' => 'a:0:{}',
+        'display_settings' => 'a:0:{}',
+        'description' => 'An example field with empty db_columns.',
+        'widget_module' => 'empty_db_columns',
+        'widget_active' => '1',
+      ],
     ];
     $tests[0]['source_data']['content_type_story'] = [
       [