Null pointer exception when some interval does not have data

**DRUID API:- **

host:8082/druid/v2/?Pretty

druid json query :-

** {
“filter”: {
“type”: “selector”,
“dimension”: “name”,
“value”:“abc”
},
“intervals”: “2019-02-22T09:46:14.000Z/2019-03-01T09:46:14.000Z”,
“granularity”: {
“period”: “PT2H”,
“timeZone”: “ETC/UTC”,
“type”: “period”
},
“dataSource”: “test”
“aggregations”: [
{
“fieldName”: “value”,
“name”: “first”,
“type”: “floatFirst”
},
{
“fieldName”: “__time”,
“name”: “initial”,
“type”: “longFirst”
},
{
“fieldName”: “value”,
“name”: “last”,
“type”: “floatFirst”
},
{
“fieldName”: “__time”,
“name”: “end”,
“type”: “longLast”
}
],
“queryType”: “timeseries”
}**

**ERROR **

{

"error": “Unknown exception”,

"errorMessage": null,

"errorClass": “java.lang.NullPointerException”,

"host": null

}

Can you please tell me what is wrong in this one.

**I am getting data, when i have every interval wise data, but exception when some interval does not have data. **

**To solve this problem, i have ingest data every hour wise atleast one point. am i right ? **

It is druid side issue or my side, atleast answer this one only please.