[SL.Core] Make Guard.NotNull() and DebugGuard.NotNull() generic

src/SixLabors.Core/Helpers/DebugGuard.cs

@@ -19,8 +19,10 @@ namespace SixLabors
         /// <param name="target">The target object, which cannot be null.</param>
         /// <param name="parameterName">The name of the parameter that is to be checked.</param>
         /// <exception cref="ArgumentNullException"><paramref name="target"/> is null</exception>
+        /// <typeparam name="T">The type of the object to verify</typeparam>
         [Conditional("DEBUG")]
-        public static void NotNull(object target, string parameterName)
+        public static void NotNull<T>(T target, string parameterName)
+            where T : class
         {
             if (target == null)
             {

src/SixLabors.Core/Helpers/Guard.cs

@@ -22,7 +22,9 @@ namespace SixLabors
         /// <param name="parameterName">The name of the parameter that is to be checked.</param>
         /// <param name="message">The error message, if any to add to the exception.</param>
         /// <exception cref="ArgumentNullException"><paramref name="target"/> is null</exception>
-        public static void NotNull(object target, string parameterName, string message = "")
+        /// <typeparam name="T">The type of the object to verify</typeparam>
+        public static void NotNull<T>(T target, string parameterName, string message = "")
+            where T : class
         {
             if (target == null)
             {

src/SixLabors.Core/SixLabors.Core.csproj.DotSettings

@@ -0,0 +1,2 @@
+<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=helpers/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>

tests/SixLabors.Core.Tests/Helpers/DebugGuardTests.cs

@@ -39,7 +39,7 @@ namespace SixLabors.Helpers.Tests
         {
             Assert.Throws<ArgumentNullException>(() =>
             {
-                DebugGuard.NotNull(null, "myParamName");
+                DebugGuard.NotNull((object)null, "myParamName");
             });
         }
 

tests/SixLabors.Core.Tests/Helpers/GuardTests.cs

@@ -21,7 +21,7 @@ namespace SixLabors.Helpers.Tests
         {
             Assert.Throws<ArgumentNullException>(() =>
             {
-                Guard.NotNull(null, "myParamName");
+                Guard.NotNull((object)null, "myParamName");
             });
         }
 
@@ -30,7 +30,7 @@ namespace SixLabors.Helpers.Tests
         {
             var exception = Assert.Throws<ArgumentNullException>(() =>
             {
-                Guard.NotNull(null, "myParamName", "myTestMessage");
+                Guard.NotNull((object)null, "myParamName", "myTestMessage");
             });
 
             Assert.Equal("myParamName", exception.ParamName);