fix(relations): handle null local key values in HasMany and HasOne relations

- Added null coalescing operator to prevent undefined index errors when local key is null
- Updated HasMany relation to use $pk ?? '' instead of direct array access
- Updated HasOne relation to use $result->$localKey ?? '' for safe array indexing
- Prevents potential PHP notices when foreign key values are null in database records

Author: wolf-leo

src/model/relation/HasMany.php

@@ -98,11 +98,11 @@ public function eagerlyResultSet(array &$resultSet, string $relation, array $sub
             // 关联数据封装
             foreach ($resultSet as $result) {
                 $pk = $result->$localKey;
-                if (!isset($data[$pk])) {
-                    $data[$pk] = [];
+                if (!isset($data[$pk ?? ''])) {
+                    $data[$pk ?? ''] = [];
                 }
 
-                $result->setRelation($relation, $this->resultSetBuild($data[$pk]));
+                $result->setRelation($relation, $this->resultSetBuild($data[$pk ?? '']));
             }
         }
     }

src/model/relation/HasOne.php

@@ -240,10 +240,10 @@ protected function eagerlySet(array &$resultSet, string $relation, array $subRel
             // 关联数据封装
             foreach ($resultSet as $result) {
                 // 关联模型
-                if (!isset($data[$result->$localKey])) {
+                if (!isset($data[$result->$localKey ?? ''])) {
                     $relationModel = $defaultModel;
                 } else {
-                    $relationModel = $data[$result->$localKey];
+                    $relationModel = $data[$result->$localKey ?? ''];
                 }
                 // 设置关联属性
                 if (!empty($this->bindAttr) && $relationModel) {