rename Preconditions to GrpcPreconditions
diff --git a/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
index 5c9ab04..1ad2290 100644
--- a/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
+++ b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
@@ -61,8 +61,8 @@
         /// </summary>
         public AuthInterceptorContext(string serviceUrl, string methodName)
         {
-            this.serviceUrl = Preconditions.CheckNotNull(serviceUrl);
-            this.methodName = Preconditions.CheckNotNull(methodName);
+            this.serviceUrl = GrpcPreconditions.CheckNotNull(serviceUrl);
+            this.methodName = GrpcPreconditions.CheckNotNull(methodName);
         }
 
         /// <summary>