Plugin throwing TypeError after WordPress 4.5 update

I was able to resolve the issue. Turns out I was using an older version of JS composer. Updating to the newest version broke my site so I tracked down the error and updated the html2element function to

html2element: function(html) {
            var $template, attributes = {},
                template = html;
            $template = $(template(this.model.toJSON()).trim()), _.each($template.get(0).attributes, function(attr) {
                attributes[attr.name] = attr.value
            }), this.$el.attr(attributes).html($template.html()), this.setContent(), this.renderContent()
        },

All is working well for me again! Hope this helps others.

I was still getting this error after trying the patch in Ben's answer: Uncaught TypeError: Cannot read property 'custom' of undefined

So I modified the html2element in composer-view.js as follows:

 html2element: function(html) {
        var $template, attributes = {},
            template = html;

        $template = $(template(this.model.toJSON()).trim());
        if($template.get(0))
        {
            _.each($template.get(0).attributes, function(attr) {
            attributes[attr.name] = attr.value
        })};

        this.$el.attr(attributes).html($template.html()),
        this.setContent(),
        this.renderContent()
    },