Fix issues netstandard2 errors

Author: ardalis

src/GuardClauses/GuardAgainstExpressionExtensions.cs

@@ -23,7 +23,10 @@ public static T Expression<T>(this IGuardClause guardClause,
         Func<T, bool> func,
         T input,
         string message,
-        [CallerArgumentExpression("input")] string? parameterName = null) where T : struct
+#if NET7_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+        [CallerArgumentExpression("input")]
+#endif
+    string? parameterName = null) where T : struct
     {
         if (func(input))
         {
@@ -50,7 +53,10 @@ public static async Task<T> ExpressionAsync<T>(this IGuardClause guardClause,
         Func<T, Task<bool>> func,
         T input,
         string message,
-        [CallerArgumentExpression("input")] string? parameterName = null) where T : struct
+#if NET7_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+        [CallerArgumentExpression("input")]
+#endif
+    string? parameterName = null) where T : struct
     {
         if (await func(input))
         {

src/GuardClauses/GuardAgainstOutOfRangeExtensions.cs

@@ -131,7 +131,7 @@ public static DateTime NullOrOutOfSQLDateRange(this IGuardClause guardClause,
 #else
     public static DateTime NullOrOutOfSQLDateRange(this IGuardClause guardClause,
          [NotNull][ValidatedNotNull] DateTime? input,
-         [CallerArgumentExpression("input")] string parameterName = null,
+         [CallerArgumentExpression("input")] string? parameterName = null,
          string? message = null)
 #endif
     {