Painless script_exception : ctx._source : null_pointer_exception

[achile]

Hello,
I am working with version elasticsearch 6.5.4, I added a new field to my existing index and I want to give it a value equal to the sum of some other fields. I used the following query in Kibana but it does not work, only the first field of the addition operation is recognized :

POST my_index/_update_by_query
{
"script": {
"lang": "painless",
"source": "ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_comments']"
},
"query": {
"match_all": {}
}
}

######Result :
{
"error": {
"root_cause": [
{
"type": "script_exception",
"reason": "runtime error",
"script_stack": [
"ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_comments']",
" ^---- HERE"
],
"script": "ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_comments']",
"lang": "painless"
}
],
"type": "script_exception",
"reason": "runtime error",
"script_stack": [
"ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_comments']",
" ^---- HERE"
],
"ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_comments']",
"lang": "painless",
"caused_by": {
"type": "null_pointer_exception",
"reason": null
}
},
"status": 500
}

#######

thank you.

[val (Val Crettaz)]

Are you certain that all of your documents have a non-null num_comments field?

[achile]

thank you for your reply;

The fields I would like to add are by default equal to 0 (type: long). If I change the order of the fields on the addition operation, the second field is pointed with the error.

I tested this script on other configuration and it works, now I do not know what is the origin of the problem.

just to correct:
ctx._source['num_attractivity']=ctx._source['num_comments']+ctx._source['num_reactions']

[val (Val Crettaz)]

What I meant is that if any of those two fields is not present in any source document, then it is not 0 by default, it is null. So you either need to make sure the each document has both of those fields or to protect against null pointer exceptions in your code.