Wijmo 5 [Flex Grid]

Custom Sorting with Null value accounting in sorting

HTML

<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<link rel="stylesheet" href="http://cdn.wijmo.com/5.20173.380/styles/wijmo.min.css">
<script src="http://cdn.wijmo.com/5.20173.380/controls/wijmo.min.js"></script>
<script src="http://cdn.wijmo.com/5.20173.380/controls/wijmo.input.min.js"></script>
<script src="http://cdn.wijmo.com/5.20173.380/controls/wijmo.grid.min.js"></script>
<script src="http://cdn.wijmo.com/5.20173.380/controls/wijmo.grid.filter.min.js"></script>
<script src="http://cdn.wijmo.com/5.20173.380/controls/wijmo.grid.sheet.min.js"></script>
<script src="http://cdn.wijmo.com/5.20173.380/interop/angular/wijmo.angular.min.js"></script>
<div ng-app="app" ng-controller="appCtrl">
       <wj-flex-sheet control="theSheet" style="height:500px;">
         
       </wj-flex-sheet>
    </div>

CSS

.wj-colfooters .wj-cell{
    background-color:#E1EFEF;
}

JavaScript

var data = [
           {"FullSerialNumber":"EFABCDGGH890","StockNumber":12356,"InterestValue":108,"PrincipalValue":15.25},
           {"FullSerialNumber":"CDEFGGH890AB","StockNumber":10042,"InterestValue":87.30,"PrincipalValue":23.65},
           {"FullSerialNumber":"EFGGH890ABCD","StockNumber":10047,"InterestValue":112.25,"PrincipalValue":250.00},
           {"FullSerialNumber":"ABCDEFGGH890","StockNumber":10027,"InterestValue":122.65,"PrincipalValue":17.25},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null},
{"FullSerialNumber":"EFABCDGGH890","StockNumber":12356,"InterestValue":108,"PrincipalValue":15.25},
           {"FullSerialNumber":"CDEFGGH890AB","StockNumber":10042,"InterestValue":87.30,"PrincipalValue":23.65},
           {"FullSerialNumber":"EFGGH890ABCD","StockNumber":10047,"InterestValue":112.25,"PrincipalValue":250.00},
           {"FullSerialNumber":"ABCDEFGGH890","StockNumber":10027,"InterestValue":122.65,"PrincipalValue":17.25},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null},{"FullSerialNumber":"EFABCDGGH890","StockNumber":12356,"InterestValue":108,"PrincipalValue":15.25},
           {"FullSerialNumber":"CDEFGGH890AB","StockNumber":10042,"InterestValue":87.30,"PrincipalValue":23.65},
           {"FullSerialNumber":"EFGGH890ABCD","StockNumber":10047,"InterestValue":112.25,"PrincipalValue":250.00},
           {"FullSerialNumber":"ABCDEFGGH890","StockNumber":10027,"InterestValue":122.65,"PrincipalValue":17.25},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null},
{"FullSerialNumber":null,"StockNumber":null,"InterestValue":null,"PrincipalValue":null}
        ];
        var app = angular.module('app', ['wj']);
        app.controller('appCtrl', function ($scope) {
 ...