fix #319, should default to .Name on mapping if .TypeNameMarker is null, this happens when you don't use MapFluent but manually new your mapping objects. Also throws a better exception if both .Name and .TypeNameMarker are null/empty

Author: Mpdreamz

src/Nest.Tests.Integration/Reproduce/Reproduce319Tests.cs

@@ -31,6 +31,14 @@ public void CreateIndexShouldNotThrowNullReference()
 			settings.Add("search.slowlog.threshold.fetch.warn", "1s");
 			settings.Analysis.Analyzers.Add(new KeyValuePair<string, AnalyzerBase>("keyword", new KeywordAnalyzer()));
 			settings.Analysis.Analyzers.Add(new KeyValuePair<string, AnalyzerBase>("simple", new SimpleAnalyzer()));
+			settings.Mappings.Add(new RootObjectMapping
+			{
+				Name = "my_root_object",
+				Properties = new Dictionary<string, IElasticType>
+				{
+					{"my_field", new StringMapping() { Name = "my_string_field "}}
+				}
+			});
 
 			Assert.DoesNotThrow(() =>
 			{

src/Nest/Domain/Mapping/Types/NumberMapping.cs

@@ -12,15 +12,15 @@ public class NumberMapping : IElasticType, IElasticCoreType
 		[JsonIgnore]
 		public TypeNameMarker TypeNameMarker { get; set; }
 
-    [JsonProperty(PropertyName = "name")]
-    public string Name { get; set; }
+		[JsonProperty(PropertyName = "name")]
+		public string Name { get; set; }
 
 		private TypeNameMarker __type;
 		[JsonProperty("type")]
 		public virtual TypeNameMarker Type { get { return (TypeNameMarker)(__type ?? "double"); } set { __type = value; } }
 
-    [JsonProperty("similarity")]
-    public string Similarity { get; set; }
+		[JsonProperty("similarity")]
+		public string Similarity { get; set; }
 
 		/// <summary>
 		/// The name of the field that will be stored in the index. Defaults to the property/field name.

src/Nest/Resolvers/Converters/IndexSettingsConverter.cs

@@ -110,7 +110,15 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
 				{
 					writer.WritePropertyName("mappings");
 					serializer.Serialize(writer,
-					                     indexSettings.Mappings.ToDictionary(m => m.TypeNameMarker.Resolve(settings.ConnectionSettings)));
+					                     indexSettings.Mappings.ToDictionary(m => 
+										 { 
+											 if (m.Name.IsNullOrEmpty() && m.TypeNameMarker == null)
+												 throw new DslException("{0} should have a name!".F(m.GetType()));
+
+
+											 var fieldName = m.Name;
+											 return m.TypeNameMarker != null ? m.TypeNameMarker.Resolve(settings.ConnectionSettings) : fieldName;
+										 }));
 				}
 			}
 			if (indexSettings.Warmers.Count > 0)