null is string ?

[Laboltus]

From time to time we get 500 error when use some specific set of measures and time shift. In broker response I see following error:

{
  "error": "Unknown exception",
  "errorMessage": "unsupported type STRING",
  "errorClass": "java.lang.IllegalArgumentException",
  "host": null
}

at the same time I see following error in historical log:

[ERROR] 2022-06-02 11:37:01,299 org.apache.druid.server.QueryResource logException - Unable to send query response. (com.fasterxml.jackson.databind.JsonMappingException: unsupported type STRING (through reference chain: org.apache.druid.query.Result["result"]->org.apache.druid.query.BySegmentResultValueClass["results"]->com.google.common.collect.Lists$TransformingRandomAccessList[0]))
[ERROR] 2022-06-02 11:37:01,299 org.apache.druid.server.QueryLifecycle logException - Exception while processing queryId [4485a8e9-34f8-47db-99f5-5940bf4fce32] (com.fasterxml.jackson.databind.JsonMappingException: unsupported type STRING (through reference chain: org.apache.druid.query.Result["result"]->org.apache.druid.query.BySegmentResultValueClass["results"]->com.google.common.collect.Lists$TransformingRandomAccessList[0]))
[WARN] 2022-06-02 11:37:01,301 org.eclipse.jetty.server.Http

I tried to localize what part of request triggers the error and here it is:

...
   "postAggregations":[
...
      {
         "type":"expression",
         "expression":"(if(\"!T_8\"!=0,(cast(\"!T_0\",'DOUBLE')/\"!T_8\"),null)-if(\"!T_9\"!=0,(cast(\"!T_4\",'DOUBLE')/\"!T_9\"),null))",
         "name":"_delta__media_cost_ecpc"
      },
...

If I replace any or both of 'null' with '0', the query works. Looks like the error appears in case of "expression":"null/null"

[Ans-hrfc]

Hi @Laboltus

i'm running into a similar error. I saw you closed the issue have you been able to find a workaround so that turnilo doesn't use null ?
I'm using v.1.40.2

from what i could see the problem was more about the casting to Double than the null. When i retrieve the cast the query succeed on druid (don't know how to avoid the cast from turnilo)

[Laboltus]

In our case we found out that the expression's divisor can be null on some intervals. It's not a common situation, so it's just became a known issue in our workflow. I guess the function fallback could be used as a workaround, but we haven't tested it.