Fetching Single Data JQUERY - php

Question

Imagine I have 3 data in my tbl_customer then If I click the button view, the modal will show with the data's. It's working if the button I clicked has data, Then the problem is, if the button has no data the modal didn't show. But I want to show the modal even I have no data in my button. Please help me out of this problem, thankyou!
Button: <button type="button" onclick="return chk('.$row['id'].')" class="btn btn-warning btn-xs">Add features</button>
Here's the code:
<script src = "http://code.jquery.com/jquery-1.9.1.js"></script>'
<?php
$db = mysqli_connect("localhost", "root", "", "psbr");
$rooms_f = mysqli_query($db, "SELECT * FROM room_f");
while($row = mysqli_fetch_assoc($rooms_f)) { ?>
<button type="button" onclick="return chk('.$row['id'].')" class="btn btn-warning btn-xs">Add features</button>
<?php } ?>
function chk(id)
{
var roomid = document.getElementById('text_id_' + id).value;
var dataString = 'roomid='+ roomid;
$.ajax({
type: "post",
url: "fetch_single3.php",
data:dataString,
cache:false,
success: function(data){
$("#modal_features").hide();
$("#modal_sample").slideDown();
$("#modal_sample").html(data);
}
});
return false;
}
fetch_single3
<?php
$db = mysqli_connect('localhost', 'root', '', 'psbr');
$rooms = mysqli_query($db, "SELECT * FROM rooms");
$roomid = $_POST['roomid'];
$query = mysqli_query($db, "SELECT * FROM room_f WHERE room_id='$roomid'");
?>
<link rel="stylesheet" type="text/css" href="css/feature-design.css">
<div id="modal_sample">
<h4 class="h4" style="margin: 3%;">Room Features</h4>
<button class="btn btn-info button">Add Feature</button>
<table id="features_table">
<tr>
<th width="20%">ID</th>
<th width="49%">Feature</th>
<th>Action</th>
</tr>
<?php while ($row = mysqli_fetch_array($query)) { ?>
<tr>
<td><?php echo $row['id']; ?></td>
<td><?php echo $row['feature']; ?></td>
<td><button class="btn btn-warning btn-xs">Update Feature</button> <button class="btn btn-warning btn-danger btn-xs ">Delete feature</button></td>
</tr>
<div class="add_modal" id="add_modal">
<h4 style="margin: 5%; ">Add Feature</h4>
<hr>
<label style="margin: 1%;">Enter Feature name</label>
<input type="text" id="text_featurename" name="text_featurename">
<input type="hidden" id="text_featureid" name="text_featureid" value="<?php echo $row['room_id']; ?>">
<input type="submit" name="submit" value="Submit" onclick="return add()" id="submit">
<button class="btn btn-default cbtn_addm">Close</button>
</div>
<?php } ?>
</table>
<button type="button" id="btn_c"class="btn_c">Close</button>
</div>