Why this code has findDOMNode warning first time open the dialog? - reactjs

Question

Always got this error when the first time open this dialog:
Warning: findDOMNode is deprecated in StrictMode. findDOMNode was
passed an instance of Transition which is inside StrictMode. Instead,
add a ref directly to the element you want to reference
import React, { Component } from "react";
import {Button, Modal, Form} from "react-bootstrap";
class ClusterBar extends Component {
state = { show: false, clusterName: '', clusterConfigure: '' };
handleClose = () => this.setState({show: false});
handleShow = () => this.setState({show: true});
handleSave = () => {
this.setState({show: false});
console.log(this.state.clusterName, this.state.clusterConfigure);
}
handleClusterNameChange = (event) => {
this.setState({clusterName: event.target.value});
}
handleClusterConfigureChange = (event) => {
this.setState({clusterConfigure: event.target.value});
}
render() {
return(
<>
<div className="list-group">
<Button className="list-group-item list-group-item-action">cluster One</Button>
<Button className="list-group-item list-group-item-action">cluster Two</Button>
<Button className="list-group-item list-group-item-action">cluster Three</Button>
<Button className="list-group-item list-group-item-action" onClick={this.handleShow}>+</Button>
</div>
<Modal show={this.state.show} onHide={this.handleClose}>
<Modal.Header closeButton>
<Modal.Title>Add a cluster</Modal.Title>
</Modal.Header>
<Modal.Body>
<Form>
<Form.Group controlId="formClusterName">
<Form.Label>Cluster Name</Form.Label>
<Form.Control type="text" onChange={this.handleClusterNameChange} />
</Form.Group>
<Form.Group controlId="formClusterConfigure">
<Form.Label>Connnection Configure</Form.Label>
<Form.Control as="textarea" rows="3" onChange={this.handleClusterConfigureChange} />
</Form.Group>
</Form>
</Modal.Body>
<Modal.Footer>
<Button variant="secondary" onClick={this.handleClose}>
Cancel
</Button>
<Button variant="primary" onClick={this.handleSave}>
Save
</Button>
</Modal.Footer>
</Modal>
</>
)
}
}
export default ClusterBar