fix #2188, get template with alias would throw json read exception because it can't create an instance of the interface

Author: Mpdreamz

src/Nest/Domain/Alias/CreateAliasDescriptor.cs

@@ -4,6 +4,7 @@
 
 namespace Nest
 {
+	[JsonConverter(typeof(ReadAsTypeConverter<CreateAliasOperation>))]
 	public interface ICreateAliasOperation
 	{
 		[JsonProperty("filter")]

src/Tests/Nest.Tests.Unit/Nest.Tests.Unit.csproj

@@ -415,6 +415,12 @@
     <None Include="Core\Update\UpdateDetectNoop.json">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Include="ObjectInitializer\Template\TemplateWithEmptyAliasResponse.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+    <None Include="ObjectInitializer\Template\TemplateWithAliasResponse.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Include="Reproduce\Issue1528_ExplicitTypeAndIndex.json">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>

src/Tests/Nest.Tests.Unit/ObjectInitializer/Template/GetTemplateRequestTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Reflection;
 using Elasticsearch.Net;
 using FluentAssertions;
 using NUnit.Framework;
@@ -25,6 +26,33 @@ public void Url()
 			this._status.RequestUrl.Should().EndWith("/_template/me-templ");
 			this._status.RequestMethod.Should().Be("GET");
 		}
+
 	}
+	[TestFixture]
+	public class GetTemplateResponseTests : BaseJsonTests
+	{
+		[Test]
+		public void HandlesResponseWithAlias()
+		{
+
+			var client = this.GetFixedReturnClient(MethodInfo.GetCurrentMethod(), "TemplateWithAliasResponse");
+			var response = client.GetTemplate("employees");
+			response.TemplateMapping.Aliases.Should().NotBeNull().And.NotBeEmpty();
+			var alias = response.TemplateMapping.Aliases.First();
+			alias.Key.Should().Be("employees");
+			alias.Value.Routing.Should().Be("name");
 
+		}
+
+		[Test]
+		public void HandlesResponseWithEmptyAlias()
+		{
+
+			var client = this.GetFixedReturnClient(MethodInfo.GetCurrentMethod(), "TemplateWithEmptyAliasResponse");
+			var response = client.GetTemplate("employees");
+			response.TemplateMapping.Aliases.Should().NotBeNull().And.NotBeEmpty();
+			var alias = response.TemplateMapping.Aliases.First();
+			alias.Key.Should().Be("employees");
+		}
+	}
 }

src/Tests/Nest.Tests.Unit/ObjectInitializer/Template/TemplateWithAliasResponse.json

@@ -0,0 +1,12 @@
+{
+  "employees": {
+    "order": 0,
+    "template": "employees-v1-*",
+    "settings": {},
+    "mappings": {},
+    "warmers": {},
+    "aliases": {
+      "employees": { "routing" :  "name" }
+    }
+  }
+}

src/Tests/Nest.Tests.Unit/ObjectInitializer/Template/TemplateWithEmptyAliasResponse.json

@@ -0,0 +1,12 @@
+{
+  "employees": {
+    "order": 0,
+    "template": "employees-v1-*",
+    "settings": {},
+    "mappings": {},
+    "warmers": {},
+    "aliases": {
+      "employees": {}
+    }
+  }
+}