     /// Message text from request JSON.
     let message: String = request.data["message", "text"]?.string ?? ""
     /// User first name from request JSON.
-    var userFirstName: String = request.data["message", "from", "first_name"]?.string ?? ""
+    let userFirstName: String = request.data["message", "from", "first_name"]?.string ?? ""
     
     /// Check if the message is empty.
     if message.isEmpty {

    
    /// Prepare the response message text.
    var response: Node = ["text": "Unknown error."]
    /// Prepare the response bytes.
    var responseData: Bytes = []
    /// Entries from request JSON.
    let entries: [JSON] = request.json?["entry"]?.array ?? []
    
    /// Iterate over all entries.
    for entry in entries {
        /// Page ID of the entry.
        let pageID: String = entry.object?["id"]?.string ?? "0"
        /// Messages from entry.
        let messaging: [JSON] = entry.object?["messaging"]?.array ?? []
        

            try responseData.set("message", response)
            
            /// Calling the Facebook API to send the response.
            let _: Response = try droplet.client.post("https://graph.facebook.com/v2.9/me/messages", query: ["access_token": messengerToken], ["Content-Type": "application/json"], Body.data(responseData.makeBytes()))
        }
    }
    
