With a payload like this,

{
  "lookup" : "StatelessKieSession",
    "commands" : [ {
      "insert" : {
        "object" : {"com.nonexisting.Person":{"name":"taro","age":"20"}},
        "out-identifier" : "person",
        "return-object" : "true",
        "entry-point" : "DEFAULT"
       }
    }, {
        "fire-all-rules" : { }
   } ]
}

if JSONMarshaller cannot find a class "com.nonexisting.Person" from classloader, it deserializes the object as a LinkedHashMap with a key "com.nonexisting.Person". It may just result in no matching rule.

https://github.com/kiegroup/droolsjbpm-integration/blob/7.52.0.Final/kie-server-parent/kie-server-api/src/main/java/org/kie/server/api/marshalling/json/JSONMarshaller.java#L807-L808

However, users may want a warning or an Exception. This JIRA is to add a system property switch to choose the behaviour.