"Uncaught TypeError: this._socket.write is not a function" on client.connect

Question

I am trying to create a OPCUA Client in nw.js with the node-opcua package. I got an error in the client.connect function. It says there is no socket.write function. Since I am using the newest nw.js and therefore node.js 11.6, it should be there, like it is discribed in the API.

I am just using the example client code to connect and logged the socket object to the console. There is in fact no "write"-function. Only a "_write"-function with different parameters is available.

My Test Connect Code (nested into async):

var testConnect = function(cb){
    client.connect(endpointUrl, function (err) {
        if(err) {
            console.log(" cannot connect to endpoint :" , endpointUrl );
        } else {
            console.log("connected !");
        }
        cb(err);
    });
}

Code that throws the error in node_modules\node-opcua-transport\src\tcp_transport.js:

TCP_transport.prototype._write_chunk = function (message_chunk) {
    if (this._socket) {
        this.bytesWritten += message_chunk.length;
        this.chunkWrittenCount ++;
        console.log(this._socket);
        this._socket.write(message_chunk);   <--- This throws the error
    }
}; 

In result the client never connects and will try it forever or till the maxRetry option value is reached.

Any thoughts?