React crashes when modal is opened

Expected behavior Open modal Actual behavior Webpage crashes when modal is opened. With example code too. Resources (screenshots, code snippets etc.)

export default class TestPage extends Component {
state = {
    modal: false
}

toggle = () => {
    this.setState({
        modal: !this.state.modal
    });
}
render() {
    return (
        <MDBContainer className={"pt-5 mt-5"}>
            <MDBBtn onClick={this.toggle}>Modal</MDBBtn>
            <MDBModal isOpen={this.state.modal} toggle={this.toggle}>
                <MDBModalHeader toggle={this.toggle}>MDBModal title</MDBModalHeader>
                <MDBModalBody>
                    (...)
                </MDBModalBody>
                <MDBModalFooter>
                    <MDBBtn color="secondary" onClick={this.toggle}>Close</MDBBtn>
                    <MDBBtn color="primary">Save changes</MDBBtn>
                </MDBModalFooter>
            </MDBModal>
        </MDBContainer>
    );
}

}