From f76a66ac059c11a2e429385b5253565de767b31d Mon Sep 17 00:00:00 2001
From: Santiago Fernandez Madero <safern@microsoft.com>
Date: Thu, 28 Mar 2019 12:15:16 -0700
Subject: [PATCH] Nullable: make Object.ToString() return nullable
 (dotnet/coreclr#23510)

Commit migrated from https://github.com/dotnet/coreclr/commit/1cdbdb09cb4938240f2358974324e77d96ff23d0
---
 .../System.Private.CoreLib/System.Private.CoreLib.csproj | 4 +++-
 .../src/System/Globalization/HijriCalendar.Win32.cs      | 4 ++--
 .../System.Private.CoreLib/src/System/Object.cs          | 2 +-
 .../src/System/String.Manipulation.cs                    | 9 +--------
 4 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
index e75a0fc2e4f3b..29811fa6d7558 100644
--- a/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -25,7 +25,9 @@
     <CLSCompliant>true</CLSCompliant>
     <WarningLevel>4</WarningLevel>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
-    <NoWarn>649,1573,1591,0419,BCL0020</NoWarn> <!-- Remove BCL0020 once https://github.com/dotnet/arcade/pull/2158 is available -->
+    <!-- Remove BCL0020 once https://github.com/dotnet/arcade/pull/2158 is available 
+         Remove CS8608 once https://github.com/dotnet/roslyn/issues/23268 is resolved -->
+    <NoWarn>649,1573,1591,0419,BCL0020,CS8609</NoWarn>
     <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
     <SignAssembly>true</SignAssembly>
     <DelaySign>true</DelaySign>
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/HijriCalendar.Win32.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/HijriCalendar.Win32.cs
index d0b645ec1c353..02e38e22edb28 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/HijriCalendar.Win32.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/HijriCalendar.Win32.cs
@@ -55,10 +55,10 @@ private static int GetAdvanceHijriDate()
                 }
 
                 int hijriAdvance = 0;
-                string str = value.ToString();
+                string? str = value.ToString();
                 if (string.Compare(str, 0, HijriAdvanceRegKeyEntry, 0, HijriAdvanceRegKeyEntry.Length, StringComparison.OrdinalIgnoreCase) == 0)
                 {
-                    if (str.Length == HijriAdvanceRegKeyEntry.Length)
+                    if (str!.Length == HijriAdvanceRegKeyEntry.Length)
                         hijriAdvance = -1;
                     else
                     {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Object.cs b/src/libraries/System.Private.CoreLib/src/System/Object.cs
index 10af793ca6ab6..2bdb5c545ab73 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Object.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Object.cs
@@ -36,7 +36,7 @@ public Object()
 
         // Returns a String which represents the object instance.  The default
         // for an object is to return the fully qualified name of the class.
-        public virtual string ToString()
+        public virtual string? ToString()
         {
             return GetType().ToString();
         }
diff --git a/src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs b/src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs
index bd56d0c33af0b..dc7f01591bb00 100644
--- a/src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs
@@ -34,14 +34,7 @@ private static unsafe void FillStringChecked(string dest, int destPos, string sr
             }
         }
 
-        public static string Concat(object? arg0)
-        {
-            if (arg0 == null)
-            {
-                return string.Empty;
-            }
-            return arg0.ToString();
-        }
+        public static string Concat(object? arg0) => arg0?.ToString() ?? string.Empty;
 
         public static string Concat(object? arg0, object? arg1)
         {