Mark .IsNullReference() extension [Obsolete]

Author: SergeiPavlov

Orm/Xtensive.Orm/Sql/Dml/Extensions.cs

@@ -4,6 +4,7 @@
 // Created by: Denis Krjuchkov
 // Created:    2009.08.24
 
+using System;
 using System.Text;
 
 namespace Xtensive.Sql.Dml
@@ -13,6 +14,22 @@ namespace Xtensive.Sql.Dml
   /// </summary>
   public static class Extensions
   {
+    /// <summary>
+    /// Determines whether the specified expression is a null reference.
+    /// Use this method instead of comparison with null,
+    /// because equality operator is overloaded for <see cref="SqlExpression"/>
+    /// to yield equality comparison expression.
+    /// </summary>
+    /// <param name="expression">The expression to check.</param>
+    /// <returns>
+    /// <see langword="true"/> if argument is a null reference; otherwise, <see langword="false"/>.
+    /// </returns>
+    [Obsolete(@"Use 'is null' operator")]
+    public static bool IsNullReference(this SqlExpression expression)
+    {
+      return ReferenceEquals(expression, null);
+    }
+
     /// <summary>
     /// Checks whether <paramref name="available"/> contains all flags of given <paramref name="required"/>.
     /// </summary>