Use ArgumentNullException.ThrowIfNull in more places

src/coreclr/System.Private.CoreLib/src/System/GC.CoreCLR.cs

@@ -291,10 +291,7 @@ public static int GetGeneration(WeakReference wo)
             object? obj = GCHandle.InternalGet(wo.WeakHandle);
             KeepAlive(wo);
 
-            if (obj is null)
-            {
-                throw new ArgumentNullException(nameof(wo));
-            }
+            ArgumentNullException.ThrowIfNull(obj, nameof(wo));
 
             return GetGeneration(obj);
         }

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/SignatureHelper.cs

@@ -276,8 +276,8 @@ private void AddOneArgTypeHelper(Type clsArgument, Type[]? requiredCustomModifie
             {
                 for (int i = 0; i < optionalCustomModifiers.Length; i++)
                 {
-                    Type t = optionalCustomModifiers[i] ??
-                        throw new ArgumentNullException(nameof(optionalCustomModifiers));
+                    Type t = optionalCustomModifiers[i];
+                    ArgumentNullException.ThrowIfNull(t, nameof(optionalCustomModifiers));
 
                     if (t.HasElementType)
                         throw new ArgumentException(SR.Argument_ArraysInvalid, nameof(optionalCustomModifiers));

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs

@@ -1879,7 +1879,7 @@ private static object CreateCustomAttributeInstance(RuntimeModule module, Runtim
         {
             if (module is null)
             {
-                throw new ArgumentNullException(SR.Arg_InvalidHandle);
+                throw new ArgumentNullException(null, SR.Arg_InvalidHandle);
             }
 
             object? result = null;
@@ -1909,7 +1909,7 @@ private static void GetPropertyOrFieldData(
         {
             if (module is null)
             {
-                throw new ArgumentNullException(SR.Arg_InvalidHandle);
+                throw new ArgumentNullException(null, SR.Arg_InvalidHandle);
             }
 
             string? nameLocal = null;

src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelDictionary.cs

@@ -49,8 +49,7 @@ public TValue this[TKey key]
         {
             get
             {
-                if (key == null)
-                    throw new ArgumentNullException(nameof(key));
+                ArgumentNullException.ThrowIfNull(key);
 
                 Entry entry = Find(key);
                 if (entry == null)
@@ -59,8 +58,7 @@ public TValue this[TKey key]
             }
             set
             {
-                if (key == null)
-                    throw new ArgumentNullException(nameof(key));
+                ArgumentNullException.ThrowIfNull(key);
 
                 _version++;
                 Entry entry = Find(key);
@@ -73,9 +71,9 @@ public TValue this[TKey key]
 
         public bool TryGetValue(TKey key, out TValue? value)
         {
+            ArgumentNullException.ThrowIfNull(key);
+
             value = default(TValue);
-            if (key == null)
-                throw new ArgumentNullException(nameof(key));
             Entry entry = Find(key);
             if (entry != null)
             {
@@ -87,8 +85,8 @@ public bool TryGetValue(TKey key, out TValue? value)
 
         public void Add(TKey key, TValue value)
         {
-            if (key == null)
-                throw new ArgumentNullException(nameof(key));
+            ArgumentNullException.ThrowIfNull(key);
+
             Entry entry = Find(key);
             if (entry != null)
                 throw new ArgumentException(SR.Format(SR.Argument_AddingDuplicate, key));
@@ -105,8 +103,8 @@ public void Clear(int capacity = DefaultSize)
 
         public bool Remove(TKey key)
         {
-            if (key == null)
-                throw new ArgumentNullException(nameof(key));
+            ArgumentNullException.ThrowIfNull(key);
+
             int bucket = GetBucket(key);
             Entry? prev = null;
             Entry? entry = _buckets[bucket];

src/coreclr/nativeaot/System.Private.CoreLib/src/System/GC.NativeAot.cs

@@ -111,10 +111,7 @@ public static int GetGeneration(WeakReference wo)
             object? obj = RuntimeImports.RhHandleGet(wo.WeakHandle);
             KeepAlive(wo);
 
-            if (obj == null)
-            {
-                throw new ArgumentNullException(nameof(wo));
-            }
+            ArgumentNullException.ThrowIfNull(obj, nameof(wo));
 
             return RuntimeImports.RhGetGeneration(obj);
         }

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/InteropServices/PInvokeMarshal.cs

@@ -348,8 +348,7 @@ public static unsafe void StringBuilderToAnsiString(System.Text.StringBuilder st
 
         public static unsafe void AnsiStringToStringBuilder(byte* newBuffer, System.Text.StringBuilder stringBuilder)
         {
-            if (newBuffer == null)
-                throw new ArgumentNullException(nameof(newBuffer));
+            ArgumentNullException.ThrowIfNull(newBuffer);
 
             int lenAnsi;
             int lenUnicode;
@@ -435,8 +434,7 @@ public static unsafe void WideCharArrayToAnsiCharArray(char[] managedArray, byte
                 return;
 
             // Desktop CLR crash (AV at runtime) - we can do better in .NET Native
-            if (pNative == null)
-                throw new ArgumentNullException(nameof(pNative));
+            ArgumentNullException.ThrowIfNull(pNative);
 
             int lenUnicode = managedArray.Length;
             fixed (char* pManaged = managedArray)

src/libraries/System.Collections.Concurrent/src/Resources/Strings.resx

@@ -126,9 +126,6 @@
   <data name="ConcurrentDictionary_KeyAlreadyExisted" xml:space="preserve">
     <value>The key already existed in the dictionary.</value>
   </data>
-  <data name="ConcurrentDictionary_ItemKeyIsNull" xml:space="preserve">
-    <value>TKey is a reference type and item.Key is null.</value>
-  </data>
   <data name="ConcurrentDictionary_TypeOfKeyIncorrect" xml:space="preserve">
     <value>The key was of an incorrect type for this dictionary.</value>
   </data>