kestra-io/kestra · error · PebbleException

The 'loopOutputs' function expects a non-null argument…

Error message

The 'loopOutputs' function expects a non-null argument 'name'.

What it means

The loopOutputs(outputs, name) function requires a non-null 'name' argument — the output key to extract from each iteration's outputs map. If name is null or absent, the function cannot determine which output field to collect from each loop iteration.

Solutions

1. Always provide the name argument: {{ loopOutputs(outputs.myLoop.outputs, 'myOutputKey') }}.
2. Ensure the name matches an actual output field defined in the loop's child task.

Example fix

# before
value: "{{ loopOutputs(outputs.myLoop.outputs) }}"
# after
value: "{{ loopOutputs(outputs.myLoop.outputs, 'result') }}"

# Always provide both arguments:
{{ loopOutputs(outputs.myLoop.outputs, 'myOutput') }}

When it happens

Trigger: Calling {{ loopOutputs(outputs.myLoop.outputs) }} without the second argument. Passing name=null or a variable that resolves to null. Using positional arguments where the second position is missing.

Common situations: The author forgets the second argument. The output name is dynamically computed from a variable that is null.

Related errors

• The 'loopOutputs' function expects a non-null argument…
• The 'isWeekend()' function expects a 'date' argument.
• The 'kv' function expects an argument 'key'.
• The 'loopOutputs' function expects 'name' to be a string.
• The 'loopOutputs' function expects 'outputs' to be a list.

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/c5a326f713ccad8c. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/functions/LoopOutputsFunction.java:47

    @Override
    public Map<String, String> getArgumentDefaults() {
        return ARGUMENT_DEFAULTS;
    }

    @Override
    public Object execute(Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) {
        Object outputsArg = args.get(ARG_OUTPUTS);
        if (outputsArg == null) {
            throw new PebbleException(null, "The 'loopOutputs' function expects a non-null argument 'outputs'.", lineNumber, self.getName());
        }
        if (!(outputsArg instanceof List<?>)) {
            throw new PebbleException(null, "The 'loopOutputs' function expects 'outputs' to be a list.", lineNumber, self.getName());
        }

        Object nameArg = args.get(ARG_NAME);
        if (nameArg == null) {
            throw new PebbleException(null, "The 'loopOutputs' function expects a non-null argument 'name'.", lineNumber, self.getName());
        }
        if (!(nameArg instanceof String)) {
            throw new PebbleException(null, "The 'loopOutputs' function expects 'name' to be a string.", lineNumber, self.getName());
        }

        String key = (String) nameArg;
        List<?> loopOutputs = (List<?>) outputsArg;
        List<Object> result = new ArrayList<>(loopOutputs.size());

        for (Object loopOutputObj : loopOutputs) {
            if (loopOutputObj instanceof Map<?, ?> loopOutput) {
                Object iterationOutputs = loopOutput.get(ITERATION_OUTPUTS_KEY);
                result.add(iterationOutputs instanceof Map<?, ?> outputs ? outputs.get(key) : null);
            } else {
                result.add(null);
            }
        }

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