Datepicker allow blank date submission

Question

I'm using datepicker with Django:

    <form method="POST" action="{% url 'approval_date_action_modal' cpname=full_id %}"> {% csrf_token %}
        <div class="input-group date" id='grm_date' data-provide="datepicker" data-date-format="yyyy-mm-dd" data-date-title="Approval Date" data-date-autoclose="true" data-date-end-date="0d" data-date-start-date="2018-11-14">
            {{ approval_form.approval_date }}
            <div class="input-group-addon">
                <span class="material-icons md-12">date_range</span>
            </div>
        </div>
        <br/>
        <input class="btn btn-primary" type="submit" value="Confirm" />
    </form>

when users clear the date and try to submit a blank date which corresponds to null in database, a warning "Please fill out this field" will pop up and cancel the submission.

Is there a simple way we can allow submission of a blank date in addition to the normal date of the stated format?