Nested field empty values aggregation returns the wrong value

[Shashi-GS (Shash)]

I have the following nested mapping for the data.
{
"index": {
"mappings": {
"type": {
"_all": {
"enabled": false
},
"properties": {
"A": {
"type": "nested",
"properties": {
"productmaster_FABRIC": {
"type": "string",
"index": "not_analyzed",
"fielddata": {
"format": "doc_values",
"loading": "eager_global_ordinals"
},
"fields": {
"hash": {
"type": "murmur3",
"precision_step": 2147483647
}
},
"null_value": "null",
"ignore_above": 10922
}
}
},
"purchaseli_QTY": {
"type": "integer"
}
}
}
}
}
}

sample data for the object is
[{purchaseli_QTY : 1, productmaster_FABRIC:"cotton"},{purchaseli_QTY : 2, productmaster_FABRIC:"polyster"}, {purchaseli_QTY : 1, productmaster_FABRIC:"rymonds"},
{purchaseli_QTY : 8, productmaster_FABRIC:""},{purchaseli_QTY : 5, productmaster_FABRIC:"cotton"},{purchaseli_QTY : 2, productmaster_FABRIC:"polyster"}, {purchaseli_QTY : 5, productmaster_FABRIC:"rymonds"},
{purchaseli_QTY : 9, productmaster_FABRIC:""},{purchaseli_QTY : 1, productmaster_FABRIC:"cotton"},{purchaseli_QTY : 2, productmaster_FABRIC:"polyster"}, {purchaseli_QTY : 1, productmaster_FABRIC:"rymonds"},
{purchaseli_QTY : 8, productmaster_FABRIC:""},{purchaseli_QTY : 1, productmaster_FABRIC:"cotton"},{purchaseli_QTY : 2, productmaster_FABRIC:"polyster"}, {purchaseli_QTY : 1, productmaster_FABRIC:"rymonds"},
{purchaseli_QTY : 8, productmaster_FABRIC:""}]

here is my query with the sum, avg or any other aggregation would return the wrong results for the empty field, other than the count aggregation.

{
	"size": 0,
	"_source": false,
	"query": {
		"filtered": {
			"filter": {
				"bool": {
					"must": [{
						"query": {
							"nested": {
								"path": "A",
								"query": {
									"term": {
										"A.productmaster_FABRIC": ""
									}
								}
							}
						}
					}]
				}
			}
		}
	},
	"aggs": {
		"sumpurchase": {
			"sum": {
				"field": "purchaseli_QTY"
			}
		}
	}
}

is any one has any idea about this issue.

I am using the elasticsearch 2.2.0 version.