def get_kernel_id(self):
        """
        Get the kernel id of the client.

        Return a str with the kernel id or None.
        """
        sessions_url = self.get_session_url()
        sessions_req = requests.get(sessions_url).content.decode()
        sessions = json.loads(sessions_req)

        if os.name == 'nt':
            path = self.path.replace('\\', '/')
        else:
            path = self.path

        for session in sessions:
            notebook_path = session.get('notebook', {}).get('path')
            if notebook_path is not None and notebook_path == path:
                kernel_id = session['kernel']['id']
                return kernel_id
Get the kernel id of the client.

        Return a str with the kernel id or None.