I don’t want to show the placeholder as a first option in the ChoiceType dropdown, using symfony 5

I have created a contact form with symfony 5.3 and I have been asked to delete the placeholder showing as a first option when you click the dropdown:

This is my Form Type code for the dropdown:

->add('department', ChoiceType::class, [
            'placeholder' => 'contact_form.department.label',
            'choices' => [
                'Unsubscribe' => 'Unsubscribe',
                'Sales' => 'Sales',
                'Marketing' => 'Marketing',
                'Customer Support' => 'Customer Support',
            ],
            'required' => true,
            'constraints' => [
                new NotBlank([
                    'message' => 'contact_form.department.not_blank',
                ]),
            ],
        ])

And the part of the twig template:

 <div class="col-md-6">
            <div class="form-select-wrapper mb-4">
                {{ form_widget(form.department, {'attr': {'class': 'form-select', 'id': 'form-select', 'required': true, 'onchange': 'showValidationMessage(this, "department-valid-feedback", "department-error")'}}) }}
                <div id="department-error" style="color: red; font-size: 14px; margin-top: 5px;">
                    {{ form_errors(form.department)|trans|raw }}
                </div>
                <div class="valid-feedback" id="department-valid-feedback" style="display: none;">
                    {{ 'Looks good!'|trans|raw }}
                </div>
            </div>
        </div>

I can’t find the solution in the symfony docs.