Missing Image issue in fabricJS groups

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.6.7/fabric.min.js"></script>
<canvas id="my-canvas"></canvas>
<button id="load-canvas">Load Canvas</button>

CSS

button {
	border: 0 none;
	background: #fff;
	border-radius: 5px;
	cursor: pointer;
	color: #333;
	box-shadow: 0 4px 6px rgba(50, 50, 93, 0.11), 0 1px 3px rgba(0, 0, 0, 0.08);
	text-transform: uppercase;
	padding: 11px 22px;
	font-weight: 600;
	font-size: 13px;
	letter-spacing: 1px;
	margin: 10px auto;
	outline: 0 none;
}

JavaScript

var canvas = new fabric.Canvas();
var el = document.getElementById('my-canvas');
var button = document.getElementById('load-canvas');

json =...