kestra-io/kestra · error · PebbleException

The 'substringAfterLast' filter expects an argument 'separat

Error message

The 'substringAfterLast' filter expects an argument 'separator'.

What it means

The 'substringAfterLast' filter returns the substring after the LAST occurrence of a separator (StringUtils.substringAfterLast). Like its sibling filters it declares 'separator' as a required named argument and throws a PebbleException when args lacks the 'separator' key at apply() time.

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/filters/SubstringAfterLastFilter.java:33

    private final List<String> argumentNames = new ArrayList<>();

    public SubstringAfterLastFilter() {
        this.argumentNames.add("separator");
    }

    @Override
    public List<String> getArgumentNames() {
        return this.argumentNames;
    }

    @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.containsKey("separator")) {
            throw new PebbleException(
                null,
                "The 'substringAfterLast' filter expects an argument 'separator'.",
                lineNumber,
                self.getName()
            );
        }

        String separator = (String) args.get("separator");
        ;

        return StringUtils.substringAfterLast(input.toString(), separator);
    }
}

View on GitHub (pinned to 823fada927)

Solutions

Supply the separator argument: {{ fileName | substringAfterLast(separator=".") }}.
Verify the separator expression is non-null, e.g. {{ x | substringAfterLast(separator=mySep ?? ".") }}.
Use a literal separator rather than a dynamic one until the template works, then reintroduce the variable.

Example fix

// before
{{ outputs.file | substringAfterLast }}
// after
{{ outputs.file | substringAfterLast(separator=".") }}

Defensive patterns

Strategy: validation

Validate before calling

{{ myVar is empty ? '' : myVar | substringAfterLast(separator=(mySep ?? ".")) }}

Prevention

Pass separator explicitly every time.
Confirm the separator variable is defined upstream.
Validate the expression in the editor before commit.

When it happens

Trigger: Invoking {{ fileName | substringAfterLast }} with no separator when the intent was to grab a file extension via {{ fileName | substringAfterLast(separator=".") }}. Also when the separator argument is bound to an undefined/null expression.

Common situations: Forgetting the argument on a less-common filter; assuming positional defaults exist (there are none); variable feeding the separator resolves to null through an optional output.

Related errors

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/6fc4188fb5c5c8a5. Report an issue: GitHub.