OpenAPITools/openapi-generator · error · RuntimeException

Empty method name (operationId) not allowed

Error message

Empty method name (operationId) not allowed

What it means

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

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AndroidClientCodegen.java:402

            example = "new " + type + "()";
        }

        if (example == null) {
            example = "null";
        } else if (Boolean.TRUE.equals(p.isArray)) {
            example = "Arrays.asList(" + example + ")";
        } else if (Boolean.TRUE.equals(p.isMap)) {
            example = "new HashMap()";
        }

        p.example = example;
    }

    @Override
    public String toOperationId(String operationId) {
        // throw exception if method name is empty
        if (StringUtils.isEmpty(operationId)) {
            throw new RuntimeException("Empty method 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;
        }

        return operationId;
    }

    @Override
    public void processOpts() {
        super.processOpts();

View on GitHub (pinned to fcec517be3)

Solutions

1. Provide a non-empty operationId for every operation in the OpenAPI spec; empty operationIds are not allowed.

When it happens

Trigger: Thrown when an operation in the OpenAPI spec has an empty or missing operationId while generating an Android 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/0a523a00bc54590c. Report an issue: GitHub.