diff --git a/src/Renci.SshNet/BaseClient.cs b/src/Renci.SshNet/BaseClient.cs
index 9d60d84ea..1751bd3cb 100644
--- a/src/Renci.SshNet/BaseClient.cs
+++ b/src/Renci.SshNet/BaseClient.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
@@ -22,7 +23,7 @@ public abstract class BaseClient : IBaseClient
         private readonly IServiceFactory _serviceFactory;
         private readonly object _keepAliveLock = new object();
         private TimeSpan _keepAliveInterval;
-        private Timer _keepAliveTimer;
+        private Timer? _keepAliveTimer;
         private ConnectionInfo _connectionInfo;
         private bool _isDisposed;
 
@@ -32,7 +33,7 @@ public abstract class BaseClient : IBaseClient
         /// <value>
         /// The current session.
         /// </value>
-        internal ISession Session { get; private set; }
+        internal ISession? Session { get; private set; }
 
         /// <summary>
         /// Gets the factory for creating new services.
@@ -142,17 +143,17 @@ public TimeSpan KeepAliveInterval
         /// <summary>
         /// Occurs when an error occurred.
         /// </summary>
-        public event EventHandler<ExceptionEventArgs> ErrorOccurred;
+        public event EventHandler<ExceptionEventArgs>? ErrorOccurred;
 
         /// <summary>
         /// Occurs when host key received.
         /// </summary>
-        public event EventHandler<HostKeyEventArgs> HostKeyReceived;
+        public event EventHandler<HostKeyEventArgs>? HostKeyReceived;
 
         /// <summary>
         /// Occurs when server identification received.
         /// </summary>
-        public event EventHandler<SshIdentificationEventArgs> ServerIdentificationReceived;
+        public event EventHandler<SshIdentificationEventArgs>? ServerIdentificationReceived;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="BaseClient"/> class.
@@ -193,7 +194,7 @@ private protected BaseClient(ConnectionInfo connectionInfo, bool ownsConnectionI
                 throw new ArgumentNullException(nameof(serviceFactory));
             }
 
-            ConnectionInfo = connectionInfo;
+            _connectionInfo = connectionInfo;
             _ownsConnectionInfo = ownsConnectionInfo;
             _serviceFactory = serviceFactory;
             _keepAliveInterval = SshNet.Session.InfiniteTimeSpan;
@@ -381,17 +382,17 @@ protected virtual void OnDisconnected()
         {
         }
 
-        private void Session_ErrorOccured(object sender, ExceptionEventArgs e)
+        private void Session_ErrorOccured(object? sender, ExceptionEventArgs e)
         {
             ErrorOccurred?.Invoke(this, e);
         }
 
-        private void Session_HostKeyReceived(object sender, HostKeyEventArgs e)
+        private void Session_HostKeyReceived(object? sender, HostKeyEventArgs e)
         {
             HostKeyReceived?.Invoke(this, e);
         }
 
-        private void Session_ServerIdentificationReceived(object sender, SshIdentificationEventArgs e)
+        private void Session_ServerIdentificationReceived(object? sender, SshIdentificationEventArgs e)
         {
             ServerIdentificationReceived?.Invoke(this, e);
         }
@@ -422,14 +423,12 @@ protected virtual void Dispose(bool disposing)
 
                 Disconnect();
 
-                if (_ownsConnectionInfo && _connectionInfo is not null)
+                if (_ownsConnectionInfo)
                 {
                     if (_connectionInfo is IDisposable connectionInfoDisposable)
                     {
                         connectionInfoDisposable.Dispose();
                     }
-
-                    _connectionInfo = null;
                 }
 
                 _isDisposed = true;
diff --git a/src/Renci.SshNet/IBaseClient.cs b/src/Renci.SshNet/IBaseClient.cs
index c42df3426..9feab44cc 100644
--- a/src/Renci.SshNet/IBaseClient.cs
+++ b/src/Renci.SshNet/IBaseClient.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
diff --git a/src/Renci.SshNet/ISftpClient.cs b/src/Renci.SshNet/ISftpClient.cs
index efbce934a..a47233014 100644
--- a/src/Renci.SshNet/ISftpClient.cs
+++ b/src/Renci.SshNet/ISftpClient.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
@@ -192,7 +193,7 @@ public interface ISftpClient : IBaseClient
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback asyncCallback);
+        IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback? asyncCallback);
 
         /// <summary>
         /// Begins an asynchronous file downloading into the stream.
@@ -211,7 +212,7 @@ public interface ISftpClient : IBaseClient
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback asyncCallback, object state, Action<ulong> downloadCallback = null);
+        IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback? asyncCallback, object? state, Action<ulong>? downloadCallback = null);
 
         /// <summary>
         /// Begins an asynchronous operation of retrieving list of files in remote directory.
@@ -224,7 +225,7 @@ public interface ISftpClient : IBaseClient
         /// An <see cref="IAsyncResult" /> that references the asynchronous operation.
         /// </returns>
         /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
-        IAsyncResult BeginListDirectory(string path, AsyncCallback asyncCallback, object state, Action<int> listCallback = null);
+        IAsyncResult BeginListDirectory(string path, AsyncCallback? asyncCallback, object? state, Action<int>? listCallback = null);
 
         /// <summary>
         /// Begins the synchronize directories.
@@ -240,7 +241,7 @@ public interface ISftpClient : IBaseClient
         /// <exception cref="ArgumentNullException"><paramref name="sourcePath"/> is <see langword="null"/>.</exception>
         /// <exception cref="ArgumentException"><paramref name="destinationPath"/> is <see langword="null"/> or contains only whitespace.</exception>
         /// <exception cref="SshException">If a problem occurs while copying the file.</exception>
-        IAsyncResult BeginSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, AsyncCallback asyncCallback, object state);
+        IAsyncResult BeginSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, AsyncCallback? asyncCallback, object? state);
 
         /// <summary>
         /// Begins an asynchronous uploading the stream into remote file.
@@ -289,7 +290,7 @@ public interface ISftpClient : IBaseClient
         /// If the remote file already exists, it is overwritten and truncated.
         /// </para>
         /// </remarks>
-        IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asyncCallback);
+        IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback? asyncCallback);
 
         /// <summary>
         /// Begins an asynchronous uploading the stream into remote file.
@@ -316,7 +317,7 @@ public interface ISftpClient : IBaseClient
         /// If the remote file already exists, it is overwritten and truncated.
         /// </para>
         /// </remarks>
-        IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asyncCallback, object state, Action<ulong> uploadCallback = null);
+        IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback? asyncCallback, object? state, Action<ulong>? uploadCallback = null);
 
         /// <summary>
         /// Begins an asynchronous uploading the stream into remote file.
@@ -343,7 +344,7 @@ public interface ISftpClient : IBaseClient
         /// <see cref="SshException"/>.
         /// </para>
         /// </remarks>
-        IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride, AsyncCallback asyncCallback, object state, Action<ulong> uploadCallback = null);
+        IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride, AsyncCallback? asyncCallback, object? state, Action<ulong>? uploadCallback = null);
 
         /// <summary>
         /// Changes remote directory to path.
@@ -522,7 +523,7 @@ public interface ISftpClient : IBaseClient
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        void DownloadFile(string path, Stream output, Action<ulong> downloadCallback = null);
+        void DownloadFile(string path, Stream output, Action<ulong>? downloadCallback = null);
 
         /// <summary>
         /// Ends an asynchronous file downloading into the stream.
@@ -700,7 +701,7 @@ public interface ISftpClient : IBaseClient
         /// <exception cref="SftpPermissionDeniedException">Permission to list the contents of the directory was denied by the remote host. <para>-or-</para> A SSH command was denied by the server.</exception>
         /// <exception cref="SshException">A SSH error where <see cref="Exception.Message" /> is the message from the remote host.</exception>
         /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
-        IEnumerable<ISftpFile> ListDirectory(string path, Action<int> listCallback = null);
+        IEnumerable<ISftpFile> ListDirectory(string path, Action<int>? listCallback = null);
 
         /// <summary>
         /// Asynchronously enumerates the files in remote directory.
@@ -1006,7 +1007,7 @@ public interface ISftpClient : IBaseClient
         /// <remarks>
         /// Method calls made by this method to <paramref name="input" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        void UploadFile(Stream input, string path, Action<ulong> uploadCallback = null);
+        void UploadFile(Stream input, string path, Action<ulong>? uploadCallback = null);
 
         /// <summary>
         /// Uploads stream into remote file.
@@ -1024,7 +1025,7 @@ public interface ISftpClient : IBaseClient
         /// <remarks>
         /// Method calls made by this method to <paramref name="input" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        void UploadFile(Stream input, string path, bool canOverride, Action<ulong> uploadCallback = null);
+        void UploadFile(Stream input, string path, bool canOverride, Action<ulong>? uploadCallback = null);
 
         /// <summary>
         /// Writes the specified byte array to the specified file, and closes the file.
diff --git a/src/Renci.SshNet/SftpClient.cs b/src/Renci.SshNet/SftpClient.cs
index 7d2c62165..735312636 100644
--- a/src/Renci.SshNet/SftpClient.cs
+++ b/src/Renci.SshNet/SftpClient.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
@@ -26,7 +27,7 @@ public class SftpClient : BaseClient, ISftpClient
         /// Holds the <see cref="ISftpSession"/> instance that is used to communicate to the
         /// SFTP server.
         /// </summary>
-        private ISftpSession _sftpSession;
+        private ISftpSession? _sftpSession;
 
         /// <summary>
         /// Holds the operation timeout.
@@ -154,7 +155,7 @@ public int ProtocolVersion
         /// <value>
         /// The current SFTP session.
         /// </value>
-        internal ISftpSession SftpSession
+        internal ISftpSession? SftpSession
         {
             get { return _sftpSession; }
         }
@@ -353,7 +354,7 @@ public void DeleteDirectory(string path)
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)
@@ -382,7 +383,7 @@ public void DeleteFile(string path)
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)
@@ -413,7 +414,7 @@ public async Task DeleteFileAsync(string path, CancellationToken cancellationTok
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)
@@ -540,12 +541,12 @@ public void SymbolicLink(string path, string linkPath)
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (string.IsNullOrWhiteSpace(linkPath))
             {
-                throw new ArgumentException("linkPath");
+                throw new ArgumentException(nameof(linkPath));
             }
 
             if (_sftpSession is null)
@@ -573,7 +574,7 @@ public void SymbolicLink(string path, string linkPath)
         /// <exception cref="SftpPermissionDeniedException">Permission to list the contents of the directory was denied by the remote host. <para>-or-</para> A SSH command was denied by the server.</exception>
         /// <exception cref="SshException">A SSH error where <see cref="Exception.Message" /> is the message from the remote host.</exception>
         /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
-        public IEnumerable<ISftpFile> ListDirectory(string path, Action<int> listCallback = null)
+        public IEnumerable<ISftpFile> ListDirectory(string path, Action<int>? listCallback = null)
         {
             CheckDisposed();
 
@@ -650,7 +651,7 @@ public async IAsyncEnumerable<ISftpFile> ListDirectoryAsync(string path, [Enumer
         /// An <see cref="IAsyncResult" /> that references the asynchronous operation.
         /// </returns>
         /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
-        public IAsyncResult BeginListDirectory(string path, AsyncCallback asyncCallback, object state, Action<int> listCallback = null)
+        public IAsyncResult BeginListDirectory(string path, AsyncCallback? asyncCallback, object? state, Action<int>? listCallback = null)
         {
             CheckDisposed();
 
@@ -742,7 +743,7 @@ public bool Exists(string path)
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)
@@ -798,7 +799,7 @@ public bool Exists(string path)
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        public void DownloadFile(string path, Stream output, Action<ulong> downloadCallback = null)
+        public void DownloadFile(string path, Stream output, Action<ulong>? downloadCallback = null)
         {
             CheckDisposed();
 
@@ -845,7 +846,7 @@ public IAsyncResult BeginDownloadFile(string path, Stream output)
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback asyncCallback)
+        public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback? asyncCallback)
         {
             return BeginDownloadFile(path, output, asyncCallback, state: null);
         }
@@ -867,13 +868,13 @@ public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback
         /// <remarks>
         /// Method calls made by this method to <paramref name="output" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback asyncCallback, object state, Action<ulong> downloadCallback = null)
+        public IAsyncResult BeginDownloadFile(string path, Stream output, AsyncCallback? asyncCallback, object? state, Action<ulong>? downloadCallback = null)
         {
             CheckDisposed();
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (output is null)
@@ -935,7 +936,7 @@ public void EndDownloadFile(IAsyncResult asyncResult)
         /// <remarks>
         /// Method calls made by this method to <paramref name="input" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        public void UploadFile(Stream input, string path, Action<ulong> uploadCallback = null)
+        public void UploadFile(Stream input, string path, Action<ulong>? uploadCallback = null)
         {
             UploadFile(input, path, canOverride: true, uploadCallback);
         }
@@ -956,7 +957,7 @@ public void UploadFile(Stream input, string path, Action<ulong> uploadCallback =
         /// <remarks>
         /// Method calls made by this method to <paramref name="input" />, may under certain conditions result in exceptions thrown by the stream.
         /// </remarks>
-        public void UploadFile(Stream input, string path, bool canOverride, Action<ulong> uploadCallback = null)
+        public void UploadFile(Stream input, string path, bool canOverride, Action<ulong>? uploadCallback = null)
         {
             CheckDisposed();
 
@@ -1024,7 +1025,7 @@ public IAsyncResult BeginUploadFile(Stream input, string path)
         /// If the remote file already exists, it is overwritten and truncated.
         /// </para>
         /// </remarks>
-        public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asyncCallback)
+        public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback? asyncCallback)
         {
             return BeginUploadFile(input, path, canOverride: true, asyncCallback, state: null);
         }
@@ -1054,7 +1055,7 @@ public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asy
         /// If the remote file already exists, it is overwritten and truncated.
         /// </para>
         /// </remarks>
-        public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asyncCallback, object state, Action<ulong> uploadCallback = null)
+        public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback? asyncCallback, object? state, Action<ulong>? uploadCallback = null)
         {
             return BeginUploadFile(input, path, canOverride: true, asyncCallback, state, uploadCallback);
         }
@@ -1084,7 +1085,7 @@ public IAsyncResult BeginUploadFile(Stream input, string path, AsyncCallback asy
         /// <see cref="SshException"/>.
         /// </para>
         /// </remarks>
-        public IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride, AsyncCallback asyncCallback, object state, Action<ulong> uploadCallback = null)
+        public IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride, AsyncCallback? asyncCallback, object? state, Action<ulong>? uploadCallback = null)
         {
             CheckDisposed();
 
@@ -1095,7 +1096,7 @@ public IAsyncResult BeginUploadFile(Stream input, string path, bool canOverride,
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             var flags = Flags.Write | Flags.Truncate;
@@ -1702,9 +1703,10 @@ public string[] ReadAllLines(string path, Encoding encoding)
 
             using (var stream = new StreamReader(OpenRead(path), encoding))
             {
-                while (!stream.EndOfStream)
+                string? line;
+                while ((line = stream.ReadLine()) != null)
                 {
-                    lines.Add(stream.ReadLine());
+                    lines.Add(line);
                 }
             }
 
@@ -2089,7 +2091,7 @@ public IEnumerable<FileInfo> SynchronizeDirectories(string sourcePath, string de
 
             if (string.IsNullOrWhiteSpace(destinationPath))
             {
-                throw new ArgumentException("destinationPath");
+                throw new ArgumentException(nameof(destinationPath));
             }
 
             return InternalSynchronizeDirectories(sourcePath, destinationPath, searchPattern, asynchResult: null);
@@ -2106,10 +2108,10 @@ public IEnumerable<FileInfo> SynchronizeDirectories(string sourcePath, string de
         /// <returns>
         /// An <see cref="IAsyncResult" /> that represents the asynchronous directory synchronization.
         /// </returns>
-        /// <exception cref="ArgumentNullException"><paramref name="sourcePath"/> is <see langword="null"/>.</exception>
+        /// <exception cref="ArgumentNullException"><paramref name="sourcePath"/> or <paramref name="searchPattern"/> is <see langword="null"/>.</exception>
         /// <exception cref="ArgumentException"><paramref name="destinationPath"/> is <see langword="null"/> or contains only whitespace.</exception>
         /// <exception cref="SshException">If a problem occurs while copying the file.</exception>
-        public IAsyncResult BeginSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, AsyncCallback asyncCallback, object state)
+        public IAsyncResult BeginSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, AsyncCallback? asyncCallback, object? state)
         {
             if (sourcePath is null)
             {
@@ -2118,7 +2120,12 @@ public IAsyncResult BeginSynchronizeDirectories(string sourcePath, string destin
 
             if (string.IsNullOrWhiteSpace(destinationPath))
             {
-                throw new ArgumentException("destDir");
+                throw new ArgumentException(nameof(destinationPath));
+            }
+
+            if (searchPattern is null)
+            {
+                throw new ArgumentNullException(nameof(searchPattern));
             }
 
             var asyncResult = new SftpSynchronizeDirectoriesAsyncResult(asyncCallback, state);
@@ -2160,7 +2167,7 @@ public IEnumerable<FileInfo> EndSynchronizeDirectories(IAsyncResult asyncResult)
             return ar.EndInvoke();
         }
 
-        private List<FileInfo> InternalSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, SftpSynchronizeDirectoriesAsyncResult asynchResult)
+        private List<FileInfo> InternalSynchronizeDirectories(string sourcePath, string destinationPath, string searchPattern, SftpSynchronizeDirectoriesAsyncResult? asynchResult)
         {
             if (!Directory.Exists(sourcePath))
             {
@@ -2255,7 +2262,7 @@ private List<FileInfo> InternalSynchronizeDirectories(string sourcePath, string
         /// </returns>
         /// <exception cref="ArgumentNullException"><paramref name="path" /> is <see langword="null"/>.</exception>
         /// <exception cref="SshConnectionException">Client not connected.</exception>
-        private List<ISftpFile> InternalListDirectory(string path, SftpListDirectoryAsyncResult asyncResult, Action<int> listCallback)
+        private List<ISftpFile> InternalListDirectory(string path, SftpListDirectoryAsyncResult? asyncResult, Action<int>? listCallback)
         {
             if (path is null)
             {
@@ -2322,7 +2329,7 @@ private List<ISftpFile> InternalListDirectory(string path, SftpListDirectoryAsyn
         /// <exception cref="ArgumentNullException"><paramref name="output" /> is <see langword="null"/>.</exception>
         /// <exception cref="ArgumentException"><paramref name="path" /> is <see langword="null"/> or contains whitespace.</exception>
         /// <exception cref="SshConnectionException">Client not connected.</exception>
-        private void InternalDownloadFile(string path, Stream output, SftpDownloadAsyncResult asyncResult, Action<ulong> downloadCallback)
+        private void InternalDownloadFile(string path, Stream output, SftpDownloadAsyncResult? asyncResult, Action<ulong>? downloadCallback)
         {
             if (output is null)
             {
@@ -2331,7 +2338,7 @@ private void InternalDownloadFile(string path, Stream output, SftpDownloadAsyncR
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)
@@ -2388,7 +2395,7 @@ private void InternalDownloadFile(string path, Stream output, SftpDownloadAsyncR
         /// <exception cref="ArgumentNullException"><paramref name="input" /> is <see langword="null"/>.</exception>
         /// <exception cref="ArgumentException"><paramref name="path" /> is <see langword="null"/> or contains whitespace.</exception>
         /// <exception cref="SshConnectionException">Client not connected.</exception>
-        private void InternalUploadFile(Stream input, string path, Flags flags, SftpUploadAsyncResult asyncResult, Action<ulong> uploadCallback)
+        private void InternalUploadFile(Stream input, string path, Flags flags, SftpUploadAsyncResult? asyncResult, Action<ulong>? uploadCallback)
         {
             if (input is null)
             {
@@ -2397,7 +2404,7 @@ private void InternalUploadFile(Stream input, string path, Flags flags, SftpUplo
 
             if (string.IsNullOrWhiteSpace(path))
             {
-                throw new ArgumentException("path");
+                throw new ArgumentException(nameof(path));
             }
 
             if (_sftpSession is null)