alibaba/Sentinel · warning · IllegalArgumentException

Parameter key cannot be empty

Error message

Parameter key cannot be empty

What it means

SimpleHttpRequest models an outgoing HTTP request for the simple-http transport (used for heartbeats to the dashboard). addParam rejects blank parameter keys (null/empty/whitespace per StringUtil.isBlank) with IllegalArgumentException, because parameters are collected into a Map and serialized into the query string — a blank key would produce a malformed URL.

Source

Thrown at sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/heartbeat/client/SimpleHttpRequest.java:92

    }

    public SimpleHttpRequest setParams(Map<String, String> params) {
        this.params = params;
        return this;
    }

    public Charset getCharset() {
        return charset;
    }

    public SimpleHttpRequest setCharset(Charset charset) {
        this.charset = charset;
        return this;
    }

    public SimpleHttpRequest addParam(String key, String value) {
        if (StringUtil.isBlank(key)) {
            throw new IllegalArgumentException("Parameter key cannot be empty");
        }
        if (params == null) {
            params = new HashMap<String, String>();
        }
        params.put(key, value);
        return this;
    }
}

View on GitHub (pinned to a3f40ba8e9)

Solutions

1. Filter keys before adding: skip entries where StringUtil.isBlank(key)
2. Fix the source map/config that produced an empty key (often stray delimiters in property lists)
3. Use fixed, literal parameter names when building SimpleHttpRequest manually

Example fix

// before
for (Map.Entry<String,String> e : params.entrySet()) {
    request.addParam(e.getKey(), e.getValue());
}

// after
for (Map.Entry<String,String> e : params.entrySet()) {
    if (StringUtil.isNotBlank(e.getKey())) {
        request.addParam(e.getKey(), e.getValue());
    }
}

for (Map.Entry<String,String> e : params.entrySet()) {
    if (StringUtil.isNotBlank(e.getKey())) {
        request.addParam(e.getKey(), e.getValue());
    }
}

When it happens

Trigger: request.addParam("", value) or addParam(null, value); typically when building heartbeat request parameters from a map whose keys come from dynamic config and one key is absent/empty.

Common situations: Custom heartbeat message builders; configuration maps with empty-string keys from property parsing (e.g. trailing comma in a list); tests iterating over maps without filtering.

Related errors

• Parameter key cannot be empty
• Metadata key cannot be empty
• maxSize must > 0
• Bad byte array
• Only form-encoded post request is supported

AI-assisted analysis of alibaba/Sentinel@a3f40ba8e9 (2026-08-14). Data as JSON: /api/errors/a544a35f7d7dc145. Report an issue: GitHub.