quarkusio/quarkus · error · IllegalStateException

methodName must be provided

Error message

methodName must be provided

What it means

Thrown by BuildTimeActionBuildItem.ActionBuilder.build when a build-time JSON-RPC action is registered without a method name. The method name is the key the Dev UI / MCP endpoint uses to route invocations; an action with a blank methodName cannot be addressed, so the build-time guard rejects the contribution during extension build.

Source

Thrown at extensions/devui/deployment-spi/src/main/java/io/quarkus/devui/spi/buildtime/BuildTimeActionBuildItem.java:190

        }

        public <T> ActionBuilder assistantFunction(BiFunction<Object, Map<String, String>, ?> assistantFunction) {
            if (this.function != null || this.runtimeValue != null)
                throw new IllegalStateException("Only one of runtimeValue, function or assistantFunction is allowed");
            this.assistantFunction = assistantFunction;
            return this;
        }

        public ActionBuilder runtime(RuntimeValue<?> runtimeValue) {
            if (this.function != null || this.assistantFunction != null)
                throw new IllegalStateException("Only one of runtimeValue, function or assistantFunction is allowed");
            this.runtimeValue = runtimeValue;
            return this;
        }

        public BuildTimeActionBuildItem build() {
            if (methodName == null || methodName.isBlank())
                throw new IllegalStateException("methodName must be provided");
            if (parameters.isEmpty())
                parameters = null;
            if (function != null) {
                return addAction(
                        new DeploymentJsonRpcMethod(methodName, description, parameters, autoUsage(usage, description),
                                mcpEnabledByDefault,
                                function));
            } else if (runtimeValue != null) {
                return addAction(
                        new RecordedJsonRpcMethod(methodName, description, autoUsage(usage, description),
                                mcpEnabledByDefault,
                                runtimeValue));
            } else if (assistantFunction != null) {
                return addAction(
                        new DeploymentJsonRpcMethod(methodName, description, parameters, autoUsage(usage, description),
                                mcpEnabledByDefault,
                                assistantFunction));
            } else {

View on GitHub (pinned to e1c734241f)

Solutions

1. Call .methodName("yourAction") before build()
2. If the name is dynamic, validate/fail-fast that it is non-blank upstream

Example fix

// before
BuildTimeActionBuildItem item = new BuildTimeActionBuildItem("my-extension")
    .build();
// after
BuildTimeActionBuildItem item = new BuildTimeActionBuildItem("my-extension")
    .methodName("getInfo")
    .runtime(runtimeValue)
    .build();

if (methodName == null || methodName.isBlank()) {
    throw new IllegalArgumentException("Action methodName must be non-blank");
}

try {
    item = actionBuilder.build();
} catch (IllegalStateException e) {
    if (e.getMessage().contains("methodName must be provided")) { /* supply methodName */ }
    else throw e;
}

When it happens

Trigger: Calling ActionBuilder.build() without ActionBuilder.methodName(String).

Common situations: Building the item programmatically where the method name comes from config or a constant that is unexpectedly empty/null.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Only one of runtimeValue, function or assistantFunction is a
• Either function, assistantFunction or runtimeValue must be p
• Either function or runtimeValue must be provided
• Invalid template
• FileName is mandatory, for example 'index.html'

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/f4fe9937df8b589f. Report an issue: GitHub.