alibaba/spring-cloud-alibaba · error · RuntimeException

empty after conversion [messageConverter:%s,payloadClass:%s,

Error message

empty after conversion [messageConverter:%s,payloadClass:%s,payloadObj:%s]

What it means

In RocketMQMessageConverterSupport.convertMessage2MQ, for payloads that are neither String nor byte[], the configured Spring MessageConverter is asked to serialize the payload to JSON. If fromMessage returns null, the binder throws a RuntimeException detailing the converter class, payload class, and object - the payload could not be converted to a sendable form.

Source

Thrown at spring-cloud-alibaba-starters/spring-cloud-starter-stream-rocketmq/src/main/java/com/alibaba/cloud/stream/binder/rocketmq/support/RocketMQMessageConverterSupport.java:124

	}

	private static org.apache.rocketmq.common.message.Message doConvert(String topic,
			Message<?> message) {
		Charset charset = Charset.defaultCharset();
		Object payloadObj = message.getPayload();
		byte[] payloads;
		try {
			if (payloadObj instanceof String payload) {
				payloads = payload.getBytes(charset);
			}
			else if (payloadObj instanceof byte[] payload) {
				payloads = payload;
			}
			else {
				String jsonObj = (String) MESSAGE_CONVERTER.fromMessage(message,
						payloadObj.getClass());
				if (null == jsonObj) {
					throw new RuntimeException(String.format(
							"empty after conversion [messageConverter:%s,payloadClass:%s,payloadObj:%s]",
							MESSAGE_CONVERTER.getClass(), payloadObj.getClass(),
							payloadObj));
				}
				payloads = jsonObj.getBytes(charset);
			}
		}
		catch (Exception e) {
			throw new RuntimeException("convert to RocketMQ message failed.", e);
		}
		return getAndWrapMessage(topic, message.getHeaders(), payloads);
	}

	private static org.apache.rocketmq.common.message.Message getAndWrapMessage(
			String topic, MessageHeaders headers, byte[] payloads) {
		if (topic == null || topic.length() < 1) {
			throw new IllegalArgumentException("topic must not be empty");
		}

View on GitHub (pinned to 115d590110)

Solutions

Ensure a MessageConverter that handles your payload type is registered (e.g. Jackson for POJOs).
Set the correct `contentType` header (e.g. application/json).
Convert the payload to String/byte[] before sending if no converter fits.
Debug which MESSAGE_CONVERTER is selected and why it returns null.

Example fix

// before
Message<String> ok = MessageBuilder.withPayload("hi").build();
Message<MyPojo> bad = MessageBuilder.withPayload(pojo).build(); // no converter -> [135]
// after
Message<MyPojo> good = MessageBuilder.withPayload(pojo)
    .setHeader("contentType", "application/json").build(); // Jackson converter handles it

Defensive patterns

Strategy: validation

Validate before calling

// Pre-flight conversion check for unknown payload types.
if (!(payloadObj instanceof String) && !(payloadObj instanceof byte[])) {
    Object out = MESSAGE_CONVERTER.fromMessage(message, payloadObj.getClass());
    if (out == null) {
        throw new IllegalArgumentException(
            "No MessageConverter produces output for " + payloadObj.getClass()
            + " - set contentType or register a converter (avoids [135])");
    }
}

Type guard

// Type guard narrowing known-serializable payloads.
static boolean isDirectlySerializable(Object p) {
    return p instanceof String || p instanceof byte[];
}

Prevention

Always set contentType for non-primitive payloads.
Register a converter that covers your domain types.
Pre-convert exotic payloads to String/byte[] when in doubt.

When it happens

Trigger: An outbound message has a non-String/non-byte[] payload whose MessageConverter.fromMessage(...) returns null (no converter handles the type, or it produced empty output).

Common situations: No suitable MessageConverter for the payload type; contentType header missing/mismatched so the chosen converter bails; a custom converter returning null on edge payloads; a payload object the converter cannot serialize.

Related errors

AI-assisted analysis of alibaba/spring-cloud-alibaba@115d590110 (2026-08-14). Data as JSON: /api/errors/34657ded7d787d89. Report an issue: GitHub.