kestra-io/kestra · error · PebbleException

The argument ''{0}'' is required.

Error message

The argument ''{0}'' is required.

What it means

Thrown by the 'regexReplace' Pebble filter when the required `regex` argument is null or missing. The filter needs both a pattern and a replacement; this branch fires first when the pattern is absent.

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/filters/RegexReplaceFilter.java:51

    private static final String ARGUMENT_REGEX = "regex";
    private static final String ARGUMENT_REPLACEMENT = "replacement";

    private static final List<String> ARGS = List.of(ARGUMENT_REGEX, ARGUMENT_REPLACEMENT);

    @Override
    public List<String> getArgumentNames() {
        return ARGS;
    }

    @Override
    public Object apply(Object input, Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) throws PebbleException {
        if (input == null) {
            return null;
        }

        if (args.get(ARGUMENT_REGEX) == null) {
            throw new PebbleException(
                null,
                MessageFormat.format("The argument ''{0}'' is required.", ARGUMENT_REGEX),
                lineNumber,
                self.getName()
            );
        }

        if (args.get(ARGUMENT_REPLACEMENT) == null) {
            throw new PebbleException(
                null,
                MessageFormat.format("The argument ''{0}'' is required.", ARGUMENT_REPLACEMENT),
                lineNumber,
                self.getName()
            );
        }

        String regex = args.get(ARGUMENT_REGEX).toString();
        String replacement = args.get(ARGUMENT_REPLACEMENT).toString();

View on GitHub (pinned to 823fada927)

Solutions

1. Supply both named arguments: `{{ s | regexReplace(regex="\\s+", replacement="_") }}`.
2. Default dynamic patterns: `regex=inputs.pattern ?? ".*"`.
3. Capture groups can be referenced as `$1`, `$2` in the replacement.

Example fix

# before
{{ slug | regexReplace(replacement="-") }}
# after
{{ slug | regexReplace(regex="\\s+", replacement="-") }}

# Supply both arguments:
{{ s | regexReplace(regex=inputs.pattern ?? ".*", replacement=inputs.repl ?? "") }}

{% if inputs.pattern is not null %}
  {{ s | regexReplace(regex=inputs.pattern, replacement="x") }}
{% endif %}

When it happens

Trigger: Calling `{{ s | regexReplace(replacement="x") }}` without `regex`; passing a variable for regex that resolved to null; misspelling the argument name.

Common situations: Refactoring drops the regex argument; referencing an unset input as the pattern; confusing positional vs named arguments.

Related errors

• The argument 'regex' is required.
• The argument 'regex' is required.
• The 'jq' filter expects an argument 'expression'.
• Group index {0} is out of bounds: must be >= 0.
• Group index {0} is out of bounds: the pattern has only {1} c

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/b4952da26e463e49. Report an issue: GitHub.