As example:

 
Given the following workflow:
 

{
"id": "aaa",
"version": "0.1",
"specVersion": "0.8",
"name": "Workflow name",
"description": "Workflow description",
"start": "StartState",
"functions": [

{ "name": "uniqueFunctionName", "operation": "sysout", "type": "custom" }

],
"states": [
{
"name": "StartState",
"type": "operation",
"actions": [
{
"name": "uniqueActionName",
"functionRef": {
"refName": "uniqueFunctionName",
"arguments":

{ "message": ".test" }

}
}
],
"end": true
}
]
}

 
If I remove message argument, I got a NPE on build:

java.lang.NullPointerException
at org.kie.kogito.serverless.workflow.parser.types.SysOutTypeHandler.fillAction(SysOutTypeHandler.java:39)
at org.kie.kogito.serverless.workflow.parser.types.ActionTypeHandler.getActionNode(ActionTypeHandler.java:38)

Is it possible to provide better error messaging?