未定义的索引：附加[重复]

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I started to learn PHP and created a contact form and unfortunately I came across an error with which I can not cope, so please help: / Undefined index: attach

                  <input type="text" class="form-control" name="fullname" placeholder="name" />
                  <br />
                  <input type="text" class="form-control" name="subject" placeholder="te" />
                  <br />
                  <input type="text" class="form-control" name="phone" placeholder="nr" />
                  <br />
                  <input type="email" class="form-control" name="emailid" placeholder="Email" />
                  <br />
                  <textarea rows="4" class="form-control" cols="20" name="comments" placeholder="message"></textarea>
                  <br />
                  <label class="control-label" for="attach">Załącznik</label>
                  <input type="file" name="attach" id="attach"/>
                  <?php 
                    echo '<div class="g-recaptcha" data-sitekey="'.$yourpublickey.'"></div>';
                   ?>
=========
                  <input type="submit" class="btn  btn-lg btn-success button"name="submit" value="send messgae" />          

if (isset($_FILES['attach']) && $_FILES['attach']['error'] == UPLOAD_ERR_OK)
            {
            $mail->AddAttachment($_FILES['attach']['tmp_name'], $_FILES['attach']['name']);
            {

Undefined index: attach

</div>