Issue #3098560: Base field filter operators do not include "Is empty (NULL)" and "Is not empty (NOT NULL)"

core/modules/views/src/EntityViewsData.php

@@ -578,8 +578,12 @@ protected function mapSingleFieldViewsData($table, $field_name, $field_type, $co
         }
     }
 
-    // Do post-processing for a few field types.
+    if (!$field_definition->isRequired()) {
+      // Provides "Is empty (NULL)" and "Is not empty (NOT NULL)" operators.
+      $views_field['filter']['allow empty'] = TRUE;
+    }
 
+    // Do post-processing for a few field types.
     $process_method = 'processViewsDataFor' . Container::camelize($field_type);
     if (method_exists($this, $process_method)) {
       $this->{$process_method}($table, $field_definition, $views_field, $column_name);