DateRangeExpression fix typo, TypeMapping missing SourceField, MultiSearch operation index, type should override request index, type if exists

Author: lukapor

src/Nest/Aggregations/Bucket/DateRange/DateRangeExpression.cs

@@ -34,6 +34,6 @@ public class DateRangeExpressionDescriptor
 		public DateRangeExpressionDescriptor To(DateMath to) => Assign(a => a.To = to);
 
 		string IDateRangeExpression.Key { get; set; }
-		public DateRangeExpressionDescriptor From(string key) => Assign(a => a.Key = key);
+		public DateRangeExpressionDescriptor Key(string key) => Assign(a => a.Key = key);
 	}
 }

src/Nest/Mapping/TypeMapping.cs

@@ -173,8 +173,11 @@ public TypeMappingDescriptor<T> AutoMap(IPropertyVisitor visitor = null, int max
 		/// <inheritdoc/>
 		public TypeMappingDescriptor<T> SizeField(Func<SizeFieldDescriptor, SizeFieldDescriptor> sizeFieldSelector) => Assign(a => a.SizeField = sizeFieldSelector?.Invoke(new SizeFieldDescriptor()));
 
-		/// <inheritdoc/>
-		public TypeMappingDescriptor<T> DisableSizeField(bool disabled = true) => Assign(a => a.SizeField = new SizeField { Enabled = !disabled });
+    /// <inheritdoc/>
+    public TypeMappingDescriptor<T> SourceField(Func<SourceFieldDescriptor, SourceFieldDescriptor> sourceFieldSelector) => Assign(a => a.SourceField = sourceFieldSelector?.Invoke(new SourceFieldDescriptor()));
+
+    /// <inheritdoc/>
+    public TypeMappingDescriptor<T> DisableSizeField(bool disabled = true) => Assign(a => a.SizeField = new SizeField { Enabled = !disabled });
 
 		/// <inheritdoc/>
 		public TypeMappingDescriptor<T> DisableIndexField(bool disabled = true) => Assign(a => a.IndexField = new IndexField { Enabled = !disabled });

src/Nest/Search/MultiSearch/MultiSearchJsonConverter.cs

@@ -22,13 +22,13 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
 
 			foreach (var operation in request.Operations.Values)
 			{
-				var indices = (request.Index != null && !request.Index.Equals(operation.Index))
+				var indices = operation.Index != null
 					? operation.Index
-					: null;
+					: request.Index;
 
-				var types = (request.Type != null && !request.Type.Equals(operation.Type))
+				var types = operation.Type != null
 					? operation.Type
-					: null;
+					: request.Type;
 
 				var searchType = operation.RequestParameters.GetQueryStringValue<SearchType>("search_type").GetStringValue();
 				if (searchType == "query_then_fetch")