Fix null vs empty string in InterpolatedStringHandlerArgumentAttribute XML comments (#79069)

Author: stephentoub

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/InterpolatedStringHandlerArgumentAttribute.cs

@@ -9,16 +9,16 @@ public sealed class InterpolatedStringHandlerArgumentAttribute : Attribute
     {
         /// <summary>Initializes a new instance of the <see cref="InterpolatedStringHandlerArgumentAttribute"/> class.</summary>
         /// <param name="argument">The name of the argument that should be passed to the handler.</param>
-        /// <remarks><see langword="null"/> may be used as the name of the receiver in an instance method.</remarks>
+        /// <remarks>The empty string may be used as the name of the receiver in an instance method.</remarks>
         public InterpolatedStringHandlerArgumentAttribute(string argument) => Arguments = new string[] { argument };
 
         /// <summary>Initializes a new instance of the <see cref="InterpolatedStringHandlerArgumentAttribute"/> class.</summary>
         /// <param name="arguments">The names of the arguments that should be passed to the handler.</param>
-        /// <remarks><see langword="null"/> may be used as the name of the receiver in an instance method.</remarks>
+        /// <remarks>The empty string may be used as the name of the receiver in an instance method.</remarks>
         public InterpolatedStringHandlerArgumentAttribute(params string[] arguments) => Arguments = arguments;
 
         /// <summary>Gets the names of the arguments that should be passed to the handler.</summary>
-        /// <remarks><see langword="null"/> may be used as the name of the receiver in an instance method.</remarks>
+        /// <remarks>The empty string may be used as the name of the receiver in an instance method.</remarks>
         public string[] Arguments { get; }
     }
 }