Better error message when MultiGet or MultiGetFull are called with no ids

Author: Mpdreamz

src/Nest/ElasticClient-MultiGet.cs

@@ -86,6 +86,9 @@ private ConnectionStatus _multiGetUsingDescriptor(Action<MultiGetDescriptor> mul
 			multiGetSelector(descriptor);
 			var data = @"{ ""docs"" : [";
 			var objects = new List<string>();
+
+			descriptor._GetOperations.ThrowIfEmpty("MultiGetFull called but no get operations were specified");
+
 			foreach (var g in descriptor._GetOperations)
 			{
 				string objectJson = "{";
@@ -130,6 +133,8 @@ private ConnectionStatus _multiGetUsingDescriptor(Action<MultiGetDescriptor> mul
 		private IEnumerable<T> MultiGet<T>(IEnumerable<string> ids, string path)
 			where T : class
 		{
+			ids.ThrowIfEmpty("ids");
+
 			var data = @"{{ ""ids"": {0} }}".F(this.Serialize(ids));
 			var response = this.Connection.PostSync(path + "_mget", data);