Better error message when string is null, empty or whitespace.

Author: Bart Koelman

src/CSharpGuidelinesAnalyzer/CSharpGuidelinesAnalyzer/Guard.cs

@@ -40,11 +40,11 @@ public static void NotNullNorEmpty<T>([CanBeNull] [ItemCanBeNull] IEnumerable<T>
         [ContractAnnotation("value: null => halt")]
         public static void NotNullNorWhiteSpace([CanBeNull] string value, [NotNull] [InvokerParameterName] string name)
         {
-            NotNull(value, name);
-
             if (string.IsNullOrWhiteSpace(value))
             {
-                throw new ArgumentException($"'{name}' cannot be empty or contain only whitespace.", name);
+                NotNullNorEmpty(value, name);
+
+                throw new ArgumentException($"'{name}' cannot contain only whitespace.", name);
             }
         }
     }