file array null | Laravel.io

hello,

I have a form so defined:

<form action="{{ route('create_node') }}" method="post" enctype="multipart/form-data" id="create-node-frm">

then via JS I add rows:

let html = '<div class="row"><div class="col-sm-2"><label for="material'+i+'">{{ __('Material') }}</label><i class="hover fas fa-minus-circle delete-row-btn"></i><select id="material'+i+'" name="material[]" required="required" class="form-control material">@foreach (config('belle.materials') as $material)<option value="{{ __($material) }}">{{ __($material) }}</option>@endforeach</select></div>';
            html += '<div class="col-sm-2"><div class="form-group"><label for="name'+i+'">{{ __('Name') }}</label><input type="text" class="form-control" name="name[]" id="name'+i+'" required="required" /></div></div>'
            html += '<div class="col-sm-1"><div class="form-group"><label for="qty'+i+'">{{ __('Quantity') }}</label><input type="text" id="qty'+i+'" name="qty[]" class="form-control" required="required" /></div></div>';
            html += '<div class="col-sm-1"><div class="form-group"><label for="correction'+i+'">{{ __('Correction') }}</label><input type="text" class="form-control" name="correction[]" id="correction'+i+'" required="required" /></div></div>';
            html += '<div class="col-sm-1"><div class="form-group"><label for="weight'+i+'">{{ __('Weight') }}</label><input type="text" class="form-control" name="weight[]" id="weight'+i+'" required="required" /></div></div>';
            html += '<div class="col-sm-1"><div class="form-group"><label for="thickness'+i+'">{{ __('Material thickness') }}</label><input type="text" class="form-control" name="thickness[]" id="thickness'+i+'" required="required" /></div></div>';
            html += '<div class="col-sm-1"><div class="form-group"><label for="bar_length'+i+'">{{ __('Bar length') }}</label><input type="text" class="form-control" name="bar_length[]" id="bar_length'+i+'" required="required" /></div></div>';
            html += '<div class="col-sm-3"><div class="form-group"><label for="matpicture'+i+'">{{ __('Picture') }}</label><input type="file" class="form-control" name="matpicture[]" id="matpicture'+i+'" required="required" /></div></div></div>';
            $('#create-node-frm #working-area').append(html);

all the data come correctly to the controller when I post, but when I do this:

if ($request->has('matpicture') && $request->matpicture[$k] !== null) {
                        $file = $request->file($request->matpicture[$k]);

$request->matpicture[$k] is correctly valued, but file is null. What am I doing wrong?

Thanks a lot

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