OpenAPITools/openapi-generator · error · RuntimeException

Empty method/operation name (operationId) not allowed

Error message

Empty method/operation name (operationId) not allowed

What it means

Error "Empty method/operation name (operationId) not allowed" thrown in OpenAPITools/openapi-generator.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java:189

        return super.addMustacheLambdas()
                .put("removeWhitespace", new RemoveWhitespaceLambda());
    }

    @Override
    public String escapeUnsafeCharacters(String input) {
        return input.replace("*/", "*_/").replace("/*", "/_*");
    }

    @Override
    public String escapeQuotationMark(String input) {
        return input.replace("\"", "");
    }

    @Override
    public String toOperationId(String operationId) {
        // throw exception if method name is empty
        if (StringUtils.isEmpty(operationId)) {
            throw new RuntimeException("Empty method/operation name (operationId) not allowed");
        }

        operationId = camelize(sanitizeName(operationId), LOWERCASE_FIRST_LETTER);

        // method name cannot use reserved keyword, e.g. return
        if (isReservedWord(operationId)) {
            String newOperationId = camelize("call_" + operationId, LOWERCASE_FIRST_LETTER);
            LOGGER.warn("{} (reserved word) cannot be used as method name. Renamed to {}", operationId, newOperationId);
            return newOperationId;
        }

        // operationId starts with a number
        if (operationId.matches("^\\d.*")) {
            LOGGER.warn(operationId + " (starting with a number) cannot be used as method sname. Renamed to " + camelize("call_" + operationId), true);
            operationId = camelize("call_" + operationId, LOWERCASE_FIRST_LETTER);
        }

        return operationId;

View on GitHub (pinned to fcec517be3)

Solutions

1. Provide a non-empty operationId for every operation in the OpenAPI spec.

When it happens

Trigger: Thrown when an operation in the OpenAPI spec has an empty or missing operationId while generating an Elm client. Provide a non-empty operationId for every operation.

Common situations: See trigger scenarios.

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/47b92d30a77d82fd. Report an issue: GitHub.