Add a guard against empty strings

src/GitHub.App/Authentication/CredentialManagement/CredentialSet.cs

@@ -18,10 +18,8 @@ namespace GitHub.Authentication.CredentialManagement
         public CredentialSet(string target)
             : this()
         {
-            if (string.IsNullOrEmpty(target))
-            {
-                throw new ArgumentNullException("target");
-            }
+            Guard.ArgumentNotEmptyString(target, "target");
+
             Target = target;
         }
 
@@ -102,7 +100,5 @@ namespace GitHub.Authentication.CredentialManagement
             // Clean up memory to the Enumeration pointer
             NativeMethods.CredFree(pCredentials);
         }
-
     }
-
 }

src/GitHub.Exports.Reactive/GitHub.Exports.Reactive.csproj

@@ -78,6 +78,7 @@
       <Link>Key.snk</Link>
     </None>
     <Compile Include="Helpers\ExceptionHelper.cs" />
+    <Compile Include="Helpers\Guard.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="..\..\script\SolutionInfo.cs">
       <Link>Properties\SolutionInfo.cs</Link>

src/GitHub.Exports.Reactive/Helpers/Guard.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Diagnostics;
+using System.Globalization;
+using Splat;
+
+namespace GitHub
+{
+    public static class Guard
+    {
+        /// <summary>
+        /// Validates that the string is not empty.
+        /// </summary>
+        /// <param name="value"></param>
+        public static void ArgumentNotEmptyString(string value, string name)
+        {
+            // We already know the value is not null because of NullGuard.Fody.
+            if (!string.IsNullOrWhiteSpace(value)) return;
+
+            string message = string.Format(CultureInfo.InvariantCulture, "The value for '{0}' must not be empty", name);
+#if DEBUG
+            if (!ModeDetector.InUnitTestRunner())
+            {
+                Debug.Fail(message);
+            }
+#endif
+            throw new ArgumentException("String cannot be empty", name);
+        }
+
+        [AttributeUsage(AttributeTargets.Parameter)]
+        internal sealed class ValidatedNotNullAttribute : Attribute
+        {
+        }
+    }
+}