From 63d8764a13dfca0fd63739498089dfa6227713c8 Mon Sep 17 00:00:00 2001
From: "Harish S. Kulkarni" <harishsk@microsoft.com>
Date: Mon, 10 Jun 2019 16:25:49 -0700
Subject: [PATCH] Fixed #3207. Added an exception to the parameterless
 constructor for KeyType because it doesn't make sense to use it without a
 parameter

---
 src/Microsoft.ML.Data/Data/SchemaDefinition.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Microsoft.ML.Data/Data/SchemaDefinition.cs b/src/Microsoft.ML.Data/Data/SchemaDefinition.cs
index 157d35d940..b26cd9554c 100644
--- a/src/Microsoft.ML.Data/Data/SchemaDefinition.cs
+++ b/src/Microsoft.ML.Data/Data/SchemaDefinition.cs
@@ -28,7 +28,7 @@ public sealed class KeyTypeAttribute : Attribute
         /// </remarks>
         public KeyTypeAttribute()
         {
-
+            throw Contracts.ExceptNotSupp("Using KeyType without the Count parameter is not supported");
         }
 
         /// <summary>