fix(laravel): belongs-to-many relations dont have a get-foreign-key-name method (#7589)

Author: mariantrifu

src/Laravel/Eloquent/Metadata/ModelMetadata.php

@@ -77,7 +77,7 @@ public function getAttributes(Model $model): array
         $indexes = $schema->getIndexes($table);
         $relations = $this->getRelations($model);
 
-        $foreignKeys = array_flip(array_column($relations, 'foreign_key'));
+        $foreignKeys = array_flip(array_filter(array_column($relations, 'foreign_key')));
         $attributes = [];
 
         foreach ($columns as $column) {