OpenAPITools/openapi-generator · error · RuntimeException

Empty method name (operationId) not allowed

Error message

Empty method name (operationId) not allowed

What it means

For the Objective-C client, toOperationId() refuses empty method names: if the operationId it receives is null or empty (StringUtils.isEmpty), it throws a RuntimeException (ObjcClientCodegen.java:619). In the normal pipeline DefaultCodegen synthesizes an operationId from the path and HTTP method when the spec omits it, so this throw indicates an explicitly empty/blank operationId (or a direct programmatic call) rather than a merely absent one.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ObjcClientCodegen.java:619

     */
    @Override
    public String escapeReservedWord(String name) {
        if (this.reservedWordsMappings().containsKey(name)) {
            return this.reservedWordsMappings().get(name);
        }
        return "_" + name;
    }

    @SuppressWarnings("static-method")
    public String escapeSpecialWord(String name) {
        return "var_" + name;
    }

    @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");
        }

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

        return camelize(sanitizeName(operationId), LOWERCASE_FIRST_LETTER);
    }

    @Override
    public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<ModelMap> allModels) {
        OperationMap operations = objs.getOperations();

        if (operations != null) {
            List<CodegenOperation> ops = operations.getOperation();

View on GitHub (pinned to fcec517be3)

Solutions

1. Give every operation a unique, non-empty operationId in the spec.
2. Remove the empty `operationId:` key entirely so the generator's path+method fallback can synthesize one.
3. Add a spec lint rule rejecting empty-string operationIds (distinct from absent operationIds).

Example fix

# before (api.yaml)
paths:
  /pets:
    get:
      operationId: ""
      responses: { '200': { description: ok } }
# after
paths:
  /pets:
    get:
      operationId: listPets
      responses: { '200': { description: ok } }

// reject explicitly empty operationIds (absent is fine; the generator synthesizes one)
openAPI.getPaths().forEach((path, item) -> {
  for (Operation op : item.readOperations().values()) {
    if (op.getOperationId() != null && op.getOperationId().trim().isEmpty()) {
      throw new IllegalArgumentException("Empty operationId on " + path
          + " — set a real value or delete the key");
    }
  }
});

try {
    new DefaultGenerator().opts(clientOptInput).generate();
} catch (RuntimeException e) {
    throw new BuildException("Objective-C generation failed: " + e.getMessage(), e);
}

When it happens

Trigger: Generating `-g objc` from a spec containing `operationId: ""` (or a whitespace-only value) on some operation; or calling ObjcClientCodegen.toOperationId("") directly in embedded usage.

Common situations: Hand-edited or templated specs where the operationId field was left as an empty string; code-gen pipelines that copy operationIds from an upstream source that sometimes emits empty values; YAML merge keys overriding operationId with an empty anchor.

Related errors

• Empty method name (operationId) not allowed
• Empty method name (operationId) not allowed
• The BLOB and JSON data types cannot be assigned a default va
• Empty database/table/column name for property '{name}' not a
• The BLOB, TEXT, GEOMETRY, and JSON data types cannot be assi

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/1e227dd1d14a505d. Report an issue: GitHub.