Add test

src/EditorFeatures/CSharpTest/UseIsNullCheck/UseIsNullCheckForReferenceEqualsTests.cs

@@ -322,6 +322,49 @@ void M(string s2)
         if (ReferenceEquals(s2, null) is null)
             return;
     }
+}");
+        }
+
+        [WorkItem(23581, "https://github.com/dotnet/roslyn/issues/23581")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseIsNullCheck)]
+        public async Task TestUnconstrainedMethodTypeParameter()
+        {
+            await TestInRegularAndScriptAsync(
+@"  
+public sealed class A
+{
+    public bool Test<T>(T a) => {|FixAllInDocument:ReferenceEquals|}(a, null);
+
+    public static void NotNull<T>(T value, string parameterName)
+    {
+        if (ReferenceEquals(value, null))
+        {
+            throw new ArgumentNullException(parameterName);
+        }
+    }
+}
+
+public class B<T>
+{
+    public bool Test(T b) => ReferenceEquals(b, null);
+}",
+@"  
+public sealed class A
+{
+    public bool Test<T>(T a) => a == null;
+
+    public static void NotNull<T>(T value, string parameterName)
+    {
+        if (value == null)
+        {
+            throw new ArgumentNullException(parameterName);
+        }
+    }
+}
+
+public class B<T>
+{
+    public bool Test(T b) => b == null;
 }");
         }
     }