diff --git a/RestSharp.sln.DotSettings b/RestSharp.sln.DotSettings
index 975adf68e..8ac5f1395 100644
--- a/RestSharp.sln.DotSettings
+++ b/RestSharp.sln.DotSettings
@@ -85,7 +85,7 @@
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=repcodes/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Serilog/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=upsert/@EntryIndexedValue">True</s:Boolean>
-	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue"> Copyright © 2009-2020 John Sheehan, Andrew Young, Alexey Zimarev and RestSharp community
+	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue"> Copyright (c) .NET Foundation and Contributors
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
diff --git a/src/Directory.Build.props b/src/Directory.Build.props
index 016a45495..c99c4fe4a 100644
--- a/src/Directory.Build.props
+++ b/src/Directory.Build.props
@@ -26,9 +26,6 @@
         <None Include="$(RepoRoot)\restsharp.png" Pack="true" PackagePath="\"/>
         <Using Include="JetBrains.Annotations"/>
     </ItemGroup>
-    <ItemGroup Condition="$(TargetFramework) == 'netstandard2.0'">
-        <PackageReference Include="IsExternalInit" Version="1.0.2" PrivateAssets="All"/>
-    </ItemGroup>
     <Target Name="CustomVersion" AfterTargets="MinVer">
         <PropertyGroup>
             <FileVersion>$(MinVerMajor).$(MinVerMinor).$(MinVerPatch)</FileVersion>
diff --git a/src/RestSharp/Parameters/BodyParameter.cs b/src/RestSharp/Parameters/BodyParameter.cs
index d2cf78531..6df933a22 100644
--- a/src/RestSharp/Parameters/BodyParameter.cs
+++ b/src/RestSharp/Parameters/BodyParameter.cs
@@ -21,15 +21,19 @@ public BodyParameter(string? name, object value, string contentType, DataFormat
         if (dataFormat == DataFormat.Binary && value is not byte[]) {
             throw new ArgumentException("Binary data format needs a byte array as value");
         }
+
         ContentType = contentType;
         DataFormat  = dataFormat;
     }
 
+    public BodyParameter(object value, string contentType, DataFormat dataFormat = DataFormat.None)
+        : this("", value, contentType, dataFormat) { }
+
     /// <summary>
     /// Body parameter data type
     /// </summary>
     public DataFormat DataFormat { get; init; } = DataFormat.None;
-    
+
     /// <summary>
     /// Custom content encoding
     /// </summary>
@@ -41,10 +45,16 @@ public XmlParameter(string name, object value, string? xmlNamespace = null, stri
         : base(name, value, contentType, DataFormat.Xml)
         => XmlNamespace = xmlNamespace;
 
+    public XmlParameter(object value, string? xmlNamespace = null, string contentType = Serializers.ContentType.Xml)
+        : this("", value, xmlNamespace, contentType) { }
+
     public string? XmlNamespace { get; }
 }
 
 public record JsonParameter : BodyParameter {
-    public JsonParameter(string name, object value, string contentType = Serializers.ContentType.Json) 
+    public JsonParameter(string name, object value, string contentType = Serializers.ContentType.Json)
         : base(name, value, contentType, DataFormat.Json) { }
-}
\ No newline at end of file
+
+    public JsonParameter(object value, string contentType = Serializers.ContentType.Json)
+        : this("", value, contentType) { }
+}
diff --git a/src/RestSharp/Properties/IsExternalInit.cs b/src/RestSharp/Properties/IsExternalInit.cs
new file mode 100644
index 000000000..deb2fb270
--- /dev/null
+++ b/src/RestSharp/Properties/IsExternalInit.cs
@@ -0,0 +1,9 @@
+#if NETSTANDARD
+using System.ComponentModel;
+
+// ReSharper disable once CheckNamespace
+namespace System.Runtime.CompilerServices;
+
+[EditorBrowsable(EditorBrowsableState.Never)]
+internal class IsExternalInit{}
+#endif
diff --git a/src/RestSharp/Request/RestRequestExtensions.cs b/src/RestSharp/Request/RestRequestExtensions.cs
index e7ccb2c01..80bfa5c13 100644
--- a/src/RestSharp/Request/RestRequestExtensions.cs
+++ b/src/RestSharp/Request/RestRequestExtensions.cs
@@ -261,6 +261,35 @@ public static RestRequest AddOrUpdateParameters(this RestRequest request, IEnume
         return request;
     }
 
+    // TODO: Three methods below added for binary compatibility with v108. Remove for the next major release.
+    // In addition, both contentType and options parameters should get default values.
+
+    public static RestRequest AddFile(
+        this RestRequest request,
+        string           name,
+        string           path,
+        string?          contentType = null
+    )
+        => request.AddFile(FileParameter.FromFile(path, name, contentType));
+
+    public static RestRequest AddFile(
+        this RestRequest request,
+        string           name,
+        byte[]           bytes,
+        string           filename,
+        string?          contentType = null
+    )
+        => request.AddFile(FileParameter.Create(name, bytes, filename, contentType));
+
+    public static RestRequest AddFile(
+        this RestRequest      request,
+        string                name,
+        Func<Stream>          getFile,
+        string                fileName,
+        string?               contentType = null
+    )
+        => request.AddFile(FileParameter.Create(name, getFile, fileName, contentType));
+
     /// <summary>
     /// Adds a file parameter to the request body. The file will be read from disk as a stream.
     /// </summary>
@@ -274,8 +303,8 @@ public static RestRequest AddFile(
         this RestRequest      request,
         string                name,
         string                path,
-        string?               contentType = null,
-        FileParameterOptions? options     = null
+        string?               contentType,
+        FileParameterOptions? options
     )
         => request.AddFile(FileParameter.FromFile(path, name, contentType, options));
 
@@ -294,8 +323,8 @@ public static RestRequest AddFile(
         string                name,
         byte[]                bytes,
         string                filename,
-        string?               contentType = null,
-        FileParameterOptions? options     = null
+        string?               contentType,
+        FileParameterOptions? options
     )
         => request.AddFile(FileParameter.Create(name, bytes, filename, contentType, options));
 
@@ -314,8 +343,8 @@ public static RestRequest AddFile(
         string                name,
         Func<Stream>          getFile,
         string                fileName,
-        string?               contentType = null,
-        FileParameterOptions? options     = null
+        string?               contentType,
+        FileParameterOptions? options
     )
         => request.AddFile(FileParameter.Create(name, getFile, fileName, contentType, options));
 
@@ -368,7 +397,7 @@ public static RestRequest AddStringBody(this RestRequest request, string body, D
     /// <param name="contentType">Content type of the body</param>
     /// <returns></returns>
     public static RestRequest AddStringBody(this RestRequest request, string body, string contentType)
-        => request.AddParameter(new BodyParameter("", body, Ensure.NotEmpty(contentType, nameof(contentType))));
+        => request.AddParameter(new BodyParameter(body, Ensure.NotEmpty(contentType, nameof(contentType))));
 
     /// <summary>
     /// Adds a JSON body parameter to the request
@@ -379,7 +408,7 @@ public static RestRequest AddStringBody(this RestRequest request, string body, s
     /// <returns></returns>
     public static RestRequest AddJsonBody<T>(this RestRequest request, T obj, string contentType = ContentType.Json) where T : class {
         request.RequestFormat = DataFormat.Json;
-        return obj is string str ? request.AddStringBody(str, DataFormat.Json) : request.AddParameter(new JsonParameter("", obj, contentType));
+        return obj is string str ? request.AddStringBody(str, DataFormat.Json) : request.AddParameter(new JsonParameter(obj, contentType));
     }
 
     /// <summary>
@@ -396,7 +425,7 @@ public static RestRequest AddXmlBody<T>(this RestRequest request, T obj, string
 
         return obj is string str
             ? request.AddStringBody(str, DataFormat.Xml)
-            : request.AddParameter(new XmlParameter("", obj, xmlNamespace, contentType));
+            : request.AddParameter(new XmlParameter(obj, xmlNamespace, contentType));
     }
 
     /// <summary>
diff --git a/src/RestSharp/RestClient.cs b/src/RestSharp/RestClient.cs
index ec8603563..b12b00d72 100644
--- a/src/RestSharp/RestClient.cs
+++ b/src/RestSharp/RestClient.cs
@@ -125,11 +125,12 @@ public RestClient(HttpMessageHandler handler, bool disposeHandler = true) : this
 
     void ConfigureHttpClient(HttpClient httpClient) {
         if (Options.MaxTimeout > 0) httpClient.Timeout = TimeSpan.FromMilliseconds(Options.MaxTimeout);
-        if (httpClient.DefaultRequestHeaders.UserAgent.All(x => x.Product.Name != "RestSharp")) {
+
+        if (Options.UserAgent != null && httpClient.DefaultRequestHeaders.UserAgent.All(x => x.Product?.Name != Options.UserAgent)) {
             httpClient.DefaultRequestHeaders.UserAgent.ParseAdd(Options.UserAgent);
         }
-        if (Options.Expect100Continue != null)
-            httpClient.DefaultRequestHeaders.ExpectContinue = Options.Expect100Continue;
+
+        if (Options.Expect100Continue != null) httpClient.DefaultRequestHeaders.ExpectContinue = Options.Expect100Continue;
     }
 
     void ConfigureHttpMessageHandler(HttpClientHandler handler) {
@@ -139,9 +140,8 @@ void ConfigureHttpMessageHandler(HttpClientHandler handler) {
         handler.AutomaticDecompression = Options.AutomaticDecompression;
         handler.PreAuthenticate        = Options.PreAuthenticate;
         handler.AllowAutoRedirect      = Options.FollowRedirects;
-        
-        if (handler.SupportsProxy)
-            handler.Proxy = Options.Proxy;
+
+        if (handler.SupportsProxy) handler.Proxy = Options.Proxy;
 
         if (Options.RemoteCertificateValidationCallback != null)
             handler.ServerCertificateCustomValidationCallback =
@@ -178,7 +178,7 @@ public RestClient AddDefaultParameter(Parameter parameter) {
             );
 
         if (!Options.AllowMultipleDefaultParametersWithSameName &&
-            !MultiParameterTypes.Contains(parameter.Type) &&
+            !MultiParameterTypes.Contains(parameter.Type)       &&
             DefaultParameters.Any(x => x.Name == parameter.Name)) {
             throw new ArgumentException("A default parameters with the same name has already been added", nameof(parameter));
         }
@@ -237,4 +237,4 @@ public void Dispose() {
         Dispose(true);
         GC.SuppressFinalize(this);
     }
-}
\ No newline at end of file
+}
diff --git a/src/RestSharp/RestClientOptions.cs b/src/RestSharp/RestClientOptions.cs
index 64f78ffa8..43fec3f3a 100644
--- a/src/RestSharp/RestClientOptions.cs
+++ b/src/RestSharp/RestClientOptions.cs
@@ -75,7 +75,7 @@ public RestClientOptions(string baseUrl) : this(new Uri(Ensure.NotEmptyString(ba
     public bool                     FollowRedirects   { get; set; } = true;
     public bool?                    Expect100Continue { get; set; } = null;
     public CookieContainer?         CookieContainer   { get; set; }
-    public string                   UserAgent         { get; set; } = DefaultUserAgent;
+    public string?                  UserAgent         { get; set; } = DefaultUserAgent;
 
     /// <summary>
     /// Maximum request duration in milliseconds. When the request timeout is specified using <seealso cref="RestRequest.Timeout"/>,