Grandchildren aggregation in ElasticSearch 1.5

Hi there,

When I try to use children aggregation within a children aggregation, I get a NullPointerException.
I have come to know that this "grandchildren" aggregation works with ElasticSearch 2.0. I wanted to know if it works with ElasticSearch 1.5. Or, I am doing something wrong in the aggregation call.
Example call:

{
"aggs": {
"toLearner": {
"children": {
"type": "learner"
},
"aggs": {
"toEL": {
"children": {
"type": "entity_learner"
},
"aggs": {
"termsId": {
"terms": {
"field": "entity"
}
}
}
}
}
}
}
}