Error filling Elasticsearch with related items

In my laravel 5.7 app I use Elasticsearch and I have bulk function to fill my votes with related vote_items.

The problem is that I that I can not add array of related vote_items as I get error :

{"error":{"root_cause":[{"type":"mapper_parsing_exception","reason":"object mapping for [vote_items] tried to parse field [null] as object, but found a concrete value"}],"type":"mapper_parsing_exception","reason":"object mapping for [vote_items] tried to parse field [null] as object, but found a concrete value"},"status":400}

at method(error line is uncomment and marked):

    public static function bulkVotesToElastic()
    {
        $elastic = app(\App\Elastic\Elastic::class);

        $elasticsearch_root_index  = config('app.elasticsearch_root_index');
        $elasticsearch_type        = with(new Vote)->getElasticsearchType();

        Vote::chunk(100, function ($Votes) use ($elastic, $elasticsearch_root_index, $elasticsearch_type) {
            foreach ($Votes as $nextVote) {

                if ($nextVote->status!= 'A') continue;   // only active votes must be saved in elasticsearch

                $voteCategory= $nextVote->voteCategory;
                if (empty($voteCategory)) continue;     // only votes with valid category must be saved in elasticsearch
                if ( !$voteCategory->active ) continue; // only votes with active category must be saved in elasticsearch

                $voteItems = VoteItem
                    ::getByVote($nextVote->id)
                    ->orderBy('ordering', 'asc')
                    ->get();
                $relatedVoteItemsList= [];
                foreach ($voteItems as $nextVoteItem) {
                    $relatedVoteItemsList[]= $nextVoteItem->name;     // THIS LINE RAISE ERROR!
//                    $relatedVoteItemsList[]= [ $nextVoteItem->name ]; // THIS LINE RAISE ERROR TOO!
//                    $relatedVoteItemsList[]= [ 'vote_item_name' => $nextVoteItem->name ];   // THIS LINE DOES NOT RAISE ERROR!
                }

                $elastic->index([
                    'index' => $elasticsearch_root_index,
                    'type'  => $elasticsearch_type,
                    'id'    => $nextVote->id,
                    'body'  => [
                        'id'          => $nextVote->id,
                        'slug'        => $nextVote->slug,
                        'name'        => $nextVote->name,
                        'description' => $nextVote->description,
                        'created_at'  => $nextVote->created_at,
                        'vote_items'  => $relatedVoteItemsList,
                        'category_id' => $voteCategory->id,
                        'category'    => [
                            'name'         => $voteCategory->name,
                            'slug'         => $voteCategory->slug,
                            'created_at'   => $voteCategory->created_at,
                        ],
                    ]
                ]);
            }
        });
    }

If I uncomment line :

//                    $relatedVoteItemsList[]= [ 'vote_item_name' => $nextVoteItem->name ];   // THIS LINE DOES NOT RAISE ERROR!

and comment 2 lines above then bulk works ok, but my search condition does not work for vote_items

$elasticQuery = [
    "bool" => [
        'must' => [
            [
                "multi_match" => [
                    "query"  => $text,
                    "type"   => "cross_fields",
                    "fields" => [
                        "name^4",
                        "description",
                        "vote_items^2"
                    ]
                ],
            ],
        ],
    ]
];

and I do not know which syntax is valid?

Thanks!

via Chebli Mohamed