conductor-oss/conductor · error · TerminateWorkflowException

Input '%s' is invalid. Cannot deserialize a list of Workflow

Error message

Input '%s' is invalid. Cannot deserialize a list of Workflow Tasks from '%s'

What it means

Thrown by getDynamicForkWorkflowTasks() when ObjectMapper.convertValue() fails to deserialize the input JSON into a List<WorkflowTask>. This happens when the input at the dynamicForkTaskParam key is not valid WorkflowTask JSON — wrong structure, missing fields, or a completely wrong type. The catch also covers the case where a deserialized task has a null taskReferenceName (the inner RuntimeException is caught by the same catch block).

Source

Thrown at core/src/main/java/com/netflix/conductor/core/execution/mapper/ForkJoinDynamicTaskMapper.java:409

                dynamicForkWorkflowTasks, (Map<String, Map<String, Object>>) dynamicForkTasksInput);
    }

    private List<WorkflowTask> getDynamicForkWorkflowTasks(
            String dynamicForkTaskParam, Map<String, Object> input) {
        Object dynamicForkTasksJson = input.get(dynamicForkTaskParam);
        try {
            List<WorkflowTask> tasks =
                    objectMapper.convertValue(dynamicForkTasksJson, ListOfWorkflowTasks);
            for (var task : tasks) {
                if (task.getTaskReferenceName() == null) {
                    throw new RuntimeException(
                            "One of the tasks had a null/missing taskReferenceName");
                }
            }
            return tasks;
        } catch (Exception e) {
            LOGGER.warn("IllegalArgumentException in getDynamicForkTasksAndInput", e);
            throw new TerminateWorkflowException(
                    String.format(
                            "Input '%s' is invalid. Cannot deserialize a list of Workflow Tasks from '%s'",
                            dynamicForkTaskParam, dynamicForkTasksJson));
        }
    }

    Pair<List<WorkflowTask>, Map<String, Map<String, Object>>> getDynamicTasksSimple(
            WorkflowTask workflowTask,
            Map<String, Object> input,
            String parentTaskName,
            boolean hasMoreThanOneFork)
            throws TerminateWorkflowException {

        String forkSubWorkflowName = (String) input.get("forkTaskWorkflow");
        String forkSubWorkflowVersionStr = (String) input.get("forkTaskWorkflowVersion");
        Integer forkSubWorkflowVersion = null;
        try {
            forkSubWorkflowVersion = Integer.parseInt(forkSubWorkflowVersionStr);

View on GitHub (pinned to cf7c3e4a8a)

Solutions

Inspect the dynamicForkTasksJson value in the error message — it shows exactly what failed to deserialize.
Ensure each element in the forked tasks array has at minimum: name, taskReferenceName, and type.
Validate the JSON structure against the WorkflowTask schema before providing it as fork task input.
If a task has a null taskReferenceName, add an explicit non-empty reference name to every forked task.

Example fix

// before — missing taskReferenceName
"forkedTasks": [
  { "name": "http_task", "type": "SIMPLE" }
]

// after
"forkedTasks": [
  { "name": "http_task", "taskReferenceName": "http_0", "type": "SIMPLE" }
]

Defensive patterns

Strategy: validation

Validate before calling

// Validate forked tasks JSON can be deserialized before execution
Object forkTasksJson = input.get(dynamicForkTaskParam);
try {
    List<WorkflowTask> tasks = objectMapper.convertValue(forkTasksJson,
        new TypeReference<List<WorkflowTask>>() {});
    for (WorkflowTask t : tasks) {
        if (t.getTaskReferenceName() == null) {
            throw new IllegalArgumentException("Missing taskReferenceName");
        }
    }
} catch (Exception e) {
    throw new IllegalArgumentException("Invalid fork tasks JSON: " + e.getMessage());
}

Prevention

Validate the dynamic fork tasks JSON against the WorkflowTask schema.
Ensure every forked task has a non-null taskReferenceName.
Use JSON schema validation on workflow input before execution.

When it happens

Trigger: The dynamic fork tasks JSON contains objects that cannot be mapped to WorkflowTask (missing required fields like name or type). The JSON is a single object instead of an array. One of the forked tasks has a null or missing taskReferenceName field.

Common situations: Workflow designer provides inline JSON for forked tasks with a typo in a field name (e.g., 'taskReference' instead of 'taskReferenceName'). The dynamic fork task list is empty or contains a string instead of a task object. A field that should be a string is provided as a number.

Related errors

AI-assisted analysis of conductor-oss/conductor@cf7c3e4a8a (2026-08-14). Data as JSON: /api/errors/afc29137feacfd3d. Report an issue: GitHub.