Cannot read property 'isSame' of undefined when removing all the dates when in multidate mode

[tonix-tuft]

On the documentation website:

This happens with the following multidate picker after unsetting all the selected dates by clicking them one after the other:

<div class="container">
    <div class="row">
        <div class="col-sm-6">
            <div class="form-group">
                <div class="input-group date" id="datetimepicker14" data-target-input="nearest">
                    <input type="text" class="form-control datetimepicker-input" data-target="#datetimepicker14"/>
                    <div class="input-group-append" data-target="#datetimepicker14" data-toggle="datetimepicker">
                        <div class="input-group-text"><i class="fa fa-calendar"></i></div>
                    </div>
                </div>
            </div>
        </div>
        <script type="text/javascript">
            $(function () {
                $('#datetimepicker14').datetimepicker({
                    allowMultidate: true,
                    multidateSeparator: ','
                });
            });
        </script>
    </div>
</div>

[tonix-tuft]

I have created the PR. Please, merge it into master. Thank you.