Bars are showing up even when value is zero - Google Charts

I have created a monthly chart using Google charts but the bars are showing up even when the value is zero.

Here is the screenshot of it

and here is the code and I know code is vulnerable to SQL Injection. You can ignore it. This is only for testing purpose

Previously order_total_amount column was set to "VARCHAR" datatype, then someone suggested that it should set to the "INT". So I changed it from Varchar to Int. But that didn't solved the problem. Bar is still showing up despite having 0 value

     <script type="text/javascript">
      google.charts.load('current', {'packages':['bar']});
      google.charts.setOnLoadCallback(drawChart);

      function drawChart() {
        var data = google.visualization.arrayToDataTable([
          ['Monthly', 'Sales'],
          <?php   
            
    $sale_chart = "SELECT 
    SUM(IF(month = 'Jan', total, 0)) AS 'Jan',
    SUM(IF(month = 'Feb', total, 0)) AS 'Feb',
    SUM(IF(month = 'Mar', total, 0)) AS 'Mar',
    SUM(IF(month = 'Apr', total, 0)) AS 'Apr',
    SUM(IF(month = 'May', total, 0)) AS 'May',
    SUM(IF(month = 'Jun', total, 0)) AS 'Jun',
    SUM(IF(month = 'Jul', total, 0)) AS 'Jul',
    SUM(IF(month = 'Aug', total, 0)) AS 'Aug',
    SUM(IF(month = 'Sep', total, 0)) AS 'Sep',
    SUM(IF(month = 'Oct', total, 0)) AS 'Oct',
    SUM(IF(month = 'Nov', total, 0)) AS 'Nov',
    SUM(IF(month = 'Dec', total, 0)) AS 'Dec'
    FROM
    (SELECT 
        MIN(DATE_FORMAT(order_date, '%b')) AS month,
            SUM(order_total_amount) AS total
    FROM
        invoice_order
    WHERE
        user_id = '$user_id'
    GROUP BY YEAR(order_date) , MONTH(order_date)
    ORDER BY YEAR(order_date) , MONTH(order_date)) AS sale";

$sale_chart_query = mysqli_query($connection,$sale_chart) or die(mysqli_error($connection));

$sale_chart_array = mysqli_fetch_assoc($sale_chart_query);
            
          foreach($sale_chart_array as $x => $val) { ?>
          ['<?php echo $x; ?>','<?php echo $val; ?>'],
           <?php } ?>
        ]);

        var options = {
        
        };

        var chart = new google.charts.Bar(document.getElementById('chart_div'));

        chart.draw(data, google.charts.Bar.convertOptions(options));
      }
     </script>

After replacing zero with null, that is how it showing up the result