diff --git a/src/Renci.SshNet/ConnectionInfo.cs b/src/Renci.SshNet/ConnectionInfo.cs
index 18ca1eeb8..374708964 100644
--- a/src/Renci.SshNet/ConnectionInfo.cs
+++ b/src/Renci.SshNet/ConnectionInfo.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
@@ -79,7 +80,7 @@ public class ConnectionInfo : IConnectionInfoInternal
         /// <summary>
         /// Gets supported compression algorithms for this connection.
         /// </summary>
-        public IOrderedDictionary<string, Func<Compressor>> CompressionAlgorithms { get; }
+        public IOrderedDictionary<string, Func<Compressor>?> CompressionAlgorithms { get; }
 
         /// <summary>
         /// Gets the supported channel requests for this connection.
@@ -129,7 +130,7 @@ public class ConnectionInfo : IConnectionInfoInternal
         /// <summary>
         /// Gets proxy connection host.
         /// </summary>
-        public string ProxyHost { get; }
+        public string? ProxyHost { get; }
 
         /// <summary>
         /// Gets proxy connection port.
@@ -139,12 +140,12 @@ public class ConnectionInfo : IConnectionInfoInternal
         /// <summary>
         /// Gets proxy connection username.
         /// </summary>
-        public string ProxyUsername { get; }
+        public string? ProxyUsername { get; }
 
         /// <summary>
         /// Gets proxy connection password.
         /// </summary>
-        public string ProxyPassword { get; }
+        public string? ProxyPassword { get; }
 
         /// <summary>
         /// Gets or sets connection timeout.
@@ -219,57 +220,63 @@ public TimeSpan ChannelCloseTimeout
         /// <summary>
         /// Occurs when authentication banner is sent by the server.
         /// </summary>
-        public event EventHandler<AuthenticationBannerEventArgs> AuthenticationBanner;
+        public event EventHandler<AuthenticationBannerEventArgs>? AuthenticationBanner;
 
         /// <summary>
         /// Gets the current key exchange algorithm.
         /// </summary>
-        public string CurrentKeyExchangeAlgorithm { get; internal set; }
+        public string? CurrentKeyExchangeAlgorithm { get; internal set; }
 
         /// <summary>
         /// Gets the current server encryption.
         /// </summary>
-        public string CurrentServerEncryption { get; internal set; }
+        public string? CurrentServerEncryption { get; internal set; }
 
         /// <summary>
         /// Gets the current client encryption.
         /// </summary>
-        public string CurrentClientEncryption { get; internal set; }
+        public string? CurrentClientEncryption { get; internal set; }
 
         /// <summary>
         /// Gets the current server hash algorithm.
         /// </summary>
-        public string CurrentServerHmacAlgorithm { get; internal set; }
+        public string? CurrentServerHmacAlgorithm { get; internal set; }
 
         /// <summary>
         /// Gets the current client hash algorithm.
         /// </summary>
-        public string CurrentClientHmacAlgorithm { get; internal set; }
+        public string? CurrentClientHmacAlgorithm { get; internal set; }
 
         /// <summary>
         /// Gets the current host key algorithm.
         /// </summary>
-        public string CurrentHostKeyAlgorithm { get; internal set; }
+        public string? CurrentHostKeyAlgorithm { get; internal set; }
 
         /// <summary>
         /// Gets the current server compression algorithm.
         /// </summary>
-        public string CurrentServerCompressionAlgorithm { get; internal set; }
+        public string? CurrentServerCompressionAlgorithm { get; internal set; }
 
         /// <summary>
-        /// Gets the server version.
+        /// Gets the current client compression algorithm.
         /// </summary>
-        public string ServerVersion { get; internal set; }
+        public string? CurrentClientCompressionAlgorithm { get; internal set; }
 
         /// <summary>
-        /// Gets the client version.
+        /// Gets the server version.
         /// </summary>
-        public string ClientVersion { get; internal set; }
+        public string? ServerVersion { get; internal set; }
 
         /// <summary>
-        /// Gets the current client compression algorithm.
+        /// Gets the client version.
         /// </summary>
-        public string CurrentClientCompressionAlgorithm { get; internal set; }
+        public string ClientVersion
+        {
+            get
+            {
+                return Session.ClientVersionString;
+            }
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ConnectionInfo"/> class.
@@ -323,7 +330,7 @@ public ConnectionInfo(string host, int port, string username, params Authenticat
         /// <exception cref="ArgumentOutOfRangeException"><paramref name="proxyType"/> is not <see cref="ProxyTypes.None"/> and <paramref name="proxyPort" /> is not within <see cref="IPEndPoint.MinPort" /> and <see cref="IPEndPoint.MaxPort" />.</exception>
         /// <exception cref="ArgumentNullException"><paramref name="authenticationMethods"/> is <see langword="null"/>.</exception>
         /// <exception cref="ArgumentException">No <paramref name="authenticationMethods"/> specified.</exception>
-        public ConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword, params AuthenticationMethod[] authenticationMethods)
+        public ConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword, params AuthenticationMethod[] authenticationMethods)
         {
             ThrowHelper.ThrowIfNull(host);
             port.ValidatePort();
@@ -413,7 +420,7 @@ public ConnectionInfo(string host, int port, string username, ProxyTypes proxyTy
 #pragma warning restore SA1107 // Code should not contain multiple statements on one line
             HostKeyAlgorithms = hostAlgs;
 
-            CompressionAlgorithms = new OrderedDictionary<string, Func<Compressor>>
+            CompressionAlgorithms = new OrderedDictionary<string, Func<Compressor>?>
                 {
                     { "none", null },
                     { "zlib@openssh.com", () => new ZlibOpenSsh() },
@@ -472,7 +479,7 @@ internal void Authenticate(ISession session, IServiceFactory serviceFactory)
         /// </summary>
         /// <param name="sender">The session in which the banner message was received.</param>
         /// <param name="e">The banner message.</param>
-        void IConnectionInfoInternal.UserAuthenticationBannerReceived(object sender, MessageEventArgs<BannerMessage> e)
+        void IConnectionInfoInternal.UserAuthenticationBannerReceived(object? sender, MessageEventArgs<BannerMessage> e)
         {
             AuthenticationBanner?.Invoke(this, new AuthenticationBannerEventArgs(Username, e.Message.Message, e.Message.Language));
         }
@@ -507,6 +514,6 @@ IList<IAuthenticationMethod> IConnectionInfoInternal.AuthenticationMethods
         /// <value>
         /// The logger factory for this connection. If <see langword="null"/> then <see cref="SshNetLoggingConfiguration.LoggerFactory"/> is used.
         /// </value>
-        public ILoggerFactory LoggerFactory { get; set; }
+        public ILoggerFactory? LoggerFactory { get; set; }
     }
 }
diff --git a/src/Renci.SshNet/IConnectionInfo.cs b/src/Renci.SshNet/IConnectionInfo.cs
index 868292b5b..db3b7b6e9 100644
--- a/src/Renci.SshNet/IConnectionInfo.cs
+++ b/src/Renci.SshNet/IConnectionInfo.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Text;
 
@@ -20,7 +21,7 @@ internal interface IConnectionInfo
         /// <value>
         /// The logger factory for this connection. If <see langword="null"/> then <see cref="SshNetLoggingConfiguration.LoggerFactory"/> is used.
         /// </value>
-        public ILoggerFactory LoggerFactory { get; }
+        public ILoggerFactory? LoggerFactory { get; }
 
         /// <summary>
         /// Gets the timeout to used when waiting for a server to acknowledge closing a channel.
@@ -77,7 +78,7 @@ internal interface IConnectionInfo
         /// <summary>
         /// Gets proxy connection host.
         /// </summary>
-        string ProxyHost { get; }
+        string? ProxyHost { get; }
 
         /// <summary>
         /// Gets proxy connection port.
@@ -87,12 +88,12 @@ internal interface IConnectionInfo
         /// <summary>
         /// Gets proxy connection username.
         /// </summary>
-        string ProxyUsername { get; }
+        string? ProxyUsername { get; }
 
         /// <summary>
         /// Gets proxy connection password.
         /// </summary>
-        string ProxyPassword { get; }
+        string? ProxyPassword { get; }
 
         /// <summary>
         /// Gets the number of retry attempts when session channel creation failed.
@@ -113,6 +114,6 @@ internal interface IConnectionInfo
         /// <summary>
         /// Occurs when authentication banner is sent by the server.
         /// </summary>
-        event EventHandler<AuthenticationBannerEventArgs> AuthenticationBanner;
+        event EventHandler<AuthenticationBannerEventArgs>? AuthenticationBanner;
     }
 }
diff --git a/src/Renci.SshNet/IConnectionInfoInternal.cs b/src/Renci.SshNet/IConnectionInfoInternal.cs
index 053e36dda..59343ceb4 100644
--- a/src/Renci.SshNet/IConnectionInfoInternal.cs
+++ b/src/Renci.SshNet/IConnectionInfoInternal.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+#nullable enable
+using System.Collections.Generic;
 
 using Renci.SshNet.Messages.Authentication;
 
@@ -14,7 +15,7 @@ internal interface IConnectionInfoInternal : IConnectionInfo
         /// </summary>
         /// <param name="sender">The session in which the banner message was received.</param>
         /// <param name="e">The banner message.</param>
-        void UserAuthenticationBannerReceived(object sender, MessageEventArgs<BannerMessage> e);
+        void UserAuthenticationBannerReceived(object? sender, MessageEventArgs<BannerMessage> e);
 
         /// <summary>
         /// Gets the supported authentication methods for this connection.
diff --git a/src/Renci.SshNet/KeyboardInteractiveConnectionInfo.cs b/src/Renci.SshNet/KeyboardInteractiveConnectionInfo.cs
index 41d1dc430..fd88d224f 100644
--- a/src/Renci.SshNet/KeyboardInteractiveConnectionInfo.cs
+++ b/src/Renci.SshNet/KeyboardInteractiveConnectionInfo.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 
 using Renci.SshNet.Common;
 
@@ -14,7 +15,7 @@ public class KeyboardInteractiveConnectionInfo : ConnectionInfo, IDisposable
         /// <summary>
         /// Occurs when server prompts for more authentication information.
         /// </summary>
-        public event EventHandler<AuthenticationPromptEventArgs> AuthenticationPrompt;
+        public event EventHandler<AuthenticationPromptEventArgs>? AuthenticationPrompt;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="KeyboardInteractiveConnectionInfo"/> class.
@@ -46,7 +47,7 @@ public KeyboardInteractiveConnectionInfo(string host, int port, string username)
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, port, username, proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -61,7 +62,7 @@ public KeyboardInteractiveConnectionInfo(string host, int port, string username,
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, port, username, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -74,7 +75,7 @@ public KeyboardInteractiveConnectionInfo(string host, int port, string username,
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -88,7 +89,7 @@ public KeyboardInteractiveConnectionInfo(string host, string username, ProxyType
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -103,7 +104,7 @@ public KeyboardInteractiveConnectionInfo(string host, string username, ProxyType
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
-        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword)
+        public KeyboardInteractiveConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword)
         {
         }
@@ -119,7 +120,7 @@ public KeyboardInteractiveConnectionInfo(string host, string username, ProxyType
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
-        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword)
+        public KeyboardInteractiveConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword)
             : base(host, port, username, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword, new KeyboardInteractiveAuthenticationMethod(username))
         {
             foreach (var authenticationMethod in AuthenticationMethods)
@@ -131,7 +132,7 @@ public KeyboardInteractiveConnectionInfo(string host, int port, string username,
             }
         }
 
-        private void AuthenticationMethod_AuthenticationPrompt(object sender, AuthenticationPromptEventArgs e)
+        private void AuthenticationMethod_AuthenticationPrompt(object? sender, AuthenticationPromptEventArgs e)
         {
 #pragma warning disable MA0091 // Sender should be 'this' for instance events
             AuthenticationPrompt?.Invoke(sender, e);
diff --git a/src/Renci.SshNet/PasswordConnectionInfo.cs b/src/Renci.SshNet/PasswordConnectionInfo.cs
index 96608400a..2911f0bf6 100644
--- a/src/Renci.SshNet/PasswordConnectionInfo.cs
+++ b/src/Renci.SshNet/PasswordConnectionInfo.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Net;
 using System.Text;
 
@@ -16,7 +17,7 @@ public class PasswordConnectionInfo : ConnectionInfo, IDisposable
         /// <summary>
         /// Occurs when user's password has expired and needs to be changed.
         /// </summary>
-        public event EventHandler<AuthenticationPasswordChangeEventArgs> PasswordExpired;
+        public event EventHandler<AuthenticationPasswordChangeEventArgs>? PasswordExpired;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PasswordConnectionInfo" /> class.
@@ -56,7 +57,7 @@ public PasswordConnectionInfo(string host, int port, string username, string pas
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public PasswordConnectionInfo(string host, int port, string username, string password, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public PasswordConnectionInfo(string host, int port, string username, string password, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, port, username, Encoding.UTF8.GetBytes(password), proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -72,7 +73,7 @@ public PasswordConnectionInfo(string host, int port, string username, string pas
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public PasswordConnectionInfo(string host, int port, string username, string password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public PasswordConnectionInfo(string host, int port, string username, string password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, port, username, Encoding.UTF8.GetBytes(password), proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -86,7 +87,7 @@ public PasswordConnectionInfo(string host, int port, string username, string pas
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, DefaultPort, username, Encoding.UTF8.GetBytes(password), proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -101,7 +102,7 @@ public PasswordConnectionInfo(string host, string username, string password, Pro
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, DefaultPort, username, Encoding.UTF8.GetBytes(password), proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -117,7 +118,7 @@ public PasswordConnectionInfo(string host, string username, string password, Pro
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
-        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword)
+        public PasswordConnectionInfo(string host, string username, string password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword)
             : this(host, DefaultPort, username, Encoding.UTF8.GetBytes(password), proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword)
         {
         }
@@ -158,7 +159,7 @@ public PasswordConnectionInfo(string host, int port, string username, byte[] pas
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, port, username, password, proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -174,7 +175,7 @@ public PasswordConnectionInfo(string host, int port, string username, byte[] pas
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, port, username, password, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -188,7 +189,7 @@ public PasswordConnectionInfo(string host, int port, string username, byte[] pas
         /// <param name="proxyType">Type of the proxy.</param>
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
-        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort)
+        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort)
             : this(host, DefaultPort, username, password, proxyType, proxyHost, proxyPort, string.Empty, string.Empty)
         {
         }
@@ -203,7 +204,7 @@ public PasswordConnectionInfo(string host, string username, byte[] password, Pro
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
-        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername)
+        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername)
             : this(host, DefaultPort, username, password, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty)
         {
         }
@@ -219,7 +220,7 @@ public PasswordConnectionInfo(string host, string username, byte[] password, Pro
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
-        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword)
+        public PasswordConnectionInfo(string host, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword)
             : this(host, DefaultPort, username, password, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword)
         {
         }
@@ -236,7 +237,7 @@ public PasswordConnectionInfo(string host, string username, byte[] password, Pro
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
-        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword)
+        public PasswordConnectionInfo(string host, int port, string username, byte[] password, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword)
             : base(host, port, username, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword, new PasswordAuthenticationMethod(username, password))
         {
             foreach (var authenticationMethod in AuthenticationMethods)
@@ -248,7 +249,7 @@ public PasswordConnectionInfo(string host, int port, string username, byte[] pas
             }
         }
 
-        private void AuthenticationMethod_PasswordExpired(object sender, AuthenticationPasswordChangeEventArgs e)
+        private void AuthenticationMethod_PasswordExpired(object? sender, AuthenticationPasswordChangeEventArgs e)
         {
 #pragma warning disable MA0091 // Sender should be 'this' for instance events
             PasswordExpired?.Invoke(sender, e);
diff --git a/src/Renci.SshNet/PrivateKeyConnectionInfo.cs b/src/Renci.SshNet/PrivateKeyConnectionInfo.cs
index a76a81a7b..c93bba940 100644
--- a/src/Renci.SshNet/PrivateKeyConnectionInfo.cs
+++ b/src/Renci.SshNet/PrivateKeyConnectionInfo.cs
@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 
@@ -49,7 +50,7 @@ public PrivateKeyConnectionInfo(string host, int port, string username, params I
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, params IPrivateKeySource[] keyFiles)
             : this(host, port, username, proxyType, proxyHost, proxyPort, string.Empty, string.Empty, keyFiles)
         {
         }
@@ -65,7 +66,7 @@ public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTyp
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, params IPrivateKeySource[] keyFiles)
             : this(host, port, username, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty, keyFiles)
         {
         }
@@ -79,7 +80,7 @@ public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTyp
         /// <param name="proxyHost">The proxy host.</param>
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, params IPrivateKeySource[] keyFiles)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, string.Empty, string.Empty, keyFiles)
         {
         }
@@ -94,7 +95,7 @@ public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyTy
         /// <param name="proxyPort">The proxy port.</param>
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, params IPrivateKeySource[] keyFiles)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, proxyUsername, string.Empty, keyFiles)
         {
         }
@@ -110,7 +111,7 @@ public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyTy
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword, params IPrivateKeySource[] keyFiles)
             : this(host, DefaultPort, username, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword, keyFiles)
         {
         }
@@ -127,7 +128,7 @@ public PrivateKeyConnectionInfo(string host, string username, ProxyTypes proxyTy
         /// <param name="proxyUsername">The proxy username.</param>
         /// <param name="proxyPassword">The proxy password.</param>
         /// <param name="keyFiles">The key files.</param>
-        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string proxyHost, int proxyPort, string proxyUsername, string proxyPassword, params IPrivateKeySource[] keyFiles)
+        public PrivateKeyConnectionInfo(string host, int port, string username, ProxyTypes proxyType, string? proxyHost, int proxyPort, string? proxyUsername, string? proxyPassword, params IPrivateKeySource[] keyFiles)
             : base(host, port, username, proxyType, proxyHost, proxyPort, proxyUsername, proxyPassword, new PrivateKeyAuthenticationMethod(username, keyFiles))
         {
             KeyFiles = new Collection<IPrivateKeySource>(keyFiles);
diff --git a/src/Renci.SshNet/Session.cs b/src/Renci.SshNet/Session.cs
index 77fe9d4c2..9bacd348e 100644
--- a/src/Renci.SshNet/Session.cs
+++ b/src/Renci.SshNet/Session.cs
@@ -35,9 +35,6 @@ public sealed class Session : ISession
         internal const byte CarriageReturn = 0x0d;
         internal const byte LineFeed = 0x0a;
 
-        private static readonly string ClientVersionString =
-            "SSH-2.0-Renci.SshNet.SshClient." + ThisAssembly.NuGetPackageVersion.Replace('-', '_');
-
         /// <summary>
         /// Specifies maximum packet size defined by the protocol.
         /// </summary>
@@ -74,6 +71,9 @@ public sealed class Session : ISession
         /// </remarks>
         private const int LocalChannelDataPacketSize = 1024 * 64;
 
+        internal static readonly string ClientVersionString =
+            "SSH-2.0-Renci.SshNet.SshClient." + ThisAssembly.NuGetPackageVersion.Replace('-', '_');
+
         /// <summary>
         /// Holds the factory to use for creating new services.
         /// </summary>
@@ -594,7 +594,6 @@ public void Connect()
 
                 // Set connection versions
                 ServerVersion = ConnectionInfo.ServerVersion = serverIdentification.ToString();
-                ConnectionInfo.ClientVersion = ClientVersion;
 
                 _logger.LogInformation("Server version '{ServerIdentification}'.", serverIdentification);
 
@@ -720,7 +719,6 @@ public async Task ConnectAsync(CancellationToken cancellationToken)
 
                 // Set connection versions
                 ServerVersion = ConnectionInfo.ServerVersion = serverIdentification.ToString();
-                ConnectionInfo.ClientVersion = ClientVersion;
 
                 _logger.LogInformation("Server version '{ServerIdentification}'.", serverIdentification);