Painless script. Illegal list shortcut value [value]. For try to stup field variable

Hello all,

I tried with Painless script to create a new field from another field.

I have this code

      def p =/[^\/]+\/([^\/]+)/;
      def m = p.matcher(doc['name.keyword'].value);
       if (m.find()) {
        doc['test_name.keyword'].value =;

If i use only the return is correct is show the correct text on the kibana but i want also to be on the _doc

The error:

Caused by: java.lang.IllegalArgumentException: Illegal list shortcut value [value].
        at org.elasticsearch.painless.Def.lookupSetter( ~[?:?]
        at org.elasticsearch.painless.DefBootstrap$PIC.lookup( ~[?:?]
        at org.elasticsearch.painless.DefBootstrap$PIC.fallback( ~[?:?]
        at org.elasticsearch.painless.PainlessScript$Script.execute(if(doc['name.keyword'].size()!=0){ ...:201) ~[?:?]
        at ~[elasticsearch-7.1.1.jar:7.1.1]
        at ~[elasticsearch-7.1.1.jar:7.1.1]
        at$executeFetchPhase$3( ~[elasticsearch-7.1.1.jar:7.1.1]
        at$3.doRun( ~[elasticsearch-7.1.1.jar:7.1.1]
        at ~[elasticsearch-7.1.1.jar:7.1.1]
        at org.elasticsearch.common.util.concurrent.TimedRunnable.doRun( ~[elasticsearch-7.1.1.jar:7.1.1]
        at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun( ~[elasticsearch-7.1.1.jar:7.1.1]

I'm not sure if it's completely related but it seems you should be returning something in the case that the matcher does not match as well.