A non-numeric value encountered in laravel script

in my laravel script, In a page appear this error:

"A non-numeric value encountered (View: /home/grammer/public_html/test/core/resources/views/admin/apiServices.blade.php)"

for this line

<td></td>

my code page:

@extends('admin.layouts.master')
@section('page_icon', 'fa fa-suitcase')
@section('page_name', 'API Services')
@section('body')
    <div class="row">
        <div class="col-md-12">
            <div class="tile">
                <h3 class="tile-title">API Services List</h3>
                <table class="table table-hover">
                    <thead>
                    <tr>
                        <th>Serial</th>
                        <th>Service ID</th>
                        <th>Name</th>
                        <th>Category</th>
                        <th>Price</th>
                        <th>Min</th>
                        <th>Max</th>
                    </tr>
                    </thead>
                    <tbody>
                    @foreach($items as $key => $item)
                        <tr>
                            <td></td>
                            <td></td>
                            <td></td>
                            <td></td>
                            <td> $</td>
                            <td></td>
                            <td></td>
                        </tr>
                    @endforeach
                    </tbody>
                </table>
            </div>
        </div>
    </div>
@endsection

via Chebli Mohamed