How to Remove the Null Value at the End of a JSON - php

Question

I am doing a server-side pagination
this is my script,
$(document).ready(function() {
$('#dataTable').DataTable( {
'pagingType': 'full_numbers',
'paging' : true,
'responsive': true,
'processing': true,
'serverSide': true,
'serverMethod': 'post',
ajax: {
url: "<?php echo $this->Url->build(['action' => 'tableview']); ?>"
},
columns: [
{ data: "id" },
{ data: "product_name" },
{ data: "unit" },
{ data: "price" },
{ data: "expiry_date" },
{ data: "stock"}
]
} );
});
and here is the query for the retrieval of data from the MySQL db and converting them into JSON
## Read value
$requestData = $this->request->getData();
$row = $requestData['start'];
$rowperpage = $requestData['length'];
$columnIndex = $requestData['order'][0]['column']; // Column index
$columnName = $requestData['columns'][$columnIndex]['data']; // Column name
$columnSortOrder = $requestData['order'][0]['dir']; // asc or desc
$searchValue = mysqli_real_escape_string($con,$_POST['search']['value']); // Search value
## Search
$searchQuery = "";
if($searchValue != ''){
$searchQuery = " and (product_name like '%".$searchValue."%' or
id like '%".$searchValue."%' or
expiry_date like'%".$searchValue."%' ) ";
}
## Total number of records without filtering
$sel = mysqli_query($con,"select count(*) as allcount from products");
$records = mysqli_fetch_assoc($sel);
$totalRecords = $records['allcount'];
## Total number of record with filtering
$sel = mysqli_query($con,"select count(*) as allcount from products WHERE 1 ".$searchQuery);
$records = mysqli_fetch_assoc($sel);
$totalRecordwithFilter = $records['allcount'];
## Fetch records
$empQuery = "select * from products WHERE 1 ".$searchQuery." order by ".$columnName." ".$columnSortOrder." limit ".$row.",".$rowperpage;
$empRecords = mysqli_query($con, $empQuery);
$data = array();
while ($row = mysqli_fetch_assoc($empRecords)) {
$nested[] = array(
"id"=>$row['id'],
"product_name"=>$row['product_name'],
"unit"=>$row['unit'],
"price"=>$row['price'],
"expiry_date"=>$row['expiry_date'],
"stock"=>$row['stock']
);
}
$data = $nested;
## Response
$response = array(
"draw" => ($requestData['draw']),
"TotalRecords" => intval($totalRecords),
"TotalDisplayRecords" => intval($totalRecordwithFilter),
"Data" => $data
);
echo json_encode($response);
I am having a result of a JSON but it has a null string/value at the end making my JSON not valid.
ive tried removing the null and it makes the JSON valid. I want to know what causes the null or how can I remove it