Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/XmlNullResolver.cs

@@ -0,0 +1,29 @@
+//------------------------------------------------------------------------------
+// <copyright file="XmlNullResolver.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+
+#if !SILVERLIGHT
+using System.Net;
+#endif
+
+namespace System.Xml {
+    internal class XmlNullResolver : XmlResolver {
+        public static readonly XmlNullResolver Singleton = new XmlNullResolver();
+
+        // Private constructor ensures existing only one instance of XmlNullResolver
+        private XmlNullResolver() { }
+
+        public override Object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn) {
+            throw new XmlException(Res.Xml_NullResolver, string.Empty);
+        }
+
+#if !SILVERLIGHT
+        public override ICredentials Credentials {
+            set { /* Do nothing */ }
+        }
+#endif
+    }
+}