quarkusio/quarkus · error · IllegalArgumentException

proxyHost must not be null

Error message

proxyHost must not be null

What it means

RestClientBuilderImpl.proxyAddress(String, int) validates its arguments before storing them. A null host cannot form a proxy address, so the builder throws IllegalArgumentException 'proxyHost must not be null'. The special host value "none" is allowed to disable the proxy.

Source

Thrown at extensions/resteasy-reactive/rest-client/runtime/src/main/java/io/quarkus/rest/client/reactive/runtime/RestClientBuilderImpl.java:229

        return this;
    }

    @Override
    public RestClientBuilderImpl hostnameVerifier(HostnameVerifier hostnameVerifier) {
        clientBuilder.hostnameVerifier(hostnameVerifier);
        return this;
    }

    @Override
    public RestClientBuilderImpl followRedirects(final boolean follow) {
        this.followRedirects = follow;
        return this;
    }

    @Override
    public RestClientBuilderImpl proxyAddress(final String proxyHost, final int proxyPort) {
        if (proxyHost == null) {
            throw new IllegalArgumentException("proxyHost must not be null");
        }
        if ((proxyPort <= 0 || proxyPort > 65535) && !proxyHost.equals("none")) {
            throw new IllegalArgumentException("Invalid port number");
        }
        this.proxyHost = proxyHost;
        this.proxyPort = proxyPort;

        return this;
    }

    public RestClientBuilderImpl proxyPassword(String proxyPassword) {
        this.proxyPassword = proxyPassword;
        return this;
    }

    public RestClientBuilderImpl proxyUser(String proxyUser) {
        this.proxyUser = proxyUser;
        return this;

View on GitHub (pinned to e1c734241f)

Solutions

1. Pass "none" instead of null if you intend to disable the proxy
2. Guard the call with a null/empty check and skip proxyAddress when no host is configured
3. Fix the config source so the proxy host env var/property is actually populated

Example fix

// before
builder.proxyAddress(System.getenv("PROXY_HOST"), 8080);
// after
String host = System.getenv("PROXY_HOST");
if (host != null) {
    builder.proxyAddress(host, 8080);
}

String host = config.getProxyHost();
if (host != null && !host.isBlank()) {
    builder.proxyAddress(host, config.getProxyPort());
}

static boolean isUsableProxyHost(String h) { return h != null && !h.isBlank(); }

try {
    builder.proxyAddress(host, port);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("proxyHost must not be null")) {
        log.warn("No proxy host configured; skipping proxy");
    } else throw e;
}

When it happens

Trigger: Calling builder.proxyAddress(null, somePort) directly, or programmatically passing a null host variable sourced from an unset environment/config value.

Common situations: Reading proxy host from env/config that is unset and passing it unvalidated; code paths that compute the host conditionally but always call proxyAddress.

Related errors

• Unsupported RestClientProxy method: ${method}
• proxyHost must not be null
• Invalid port number
• Invalid proxy string. Expected <hostname>:<port>, found '${p
• Invalid proxy setting. The port is not a number in '${proxy}

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/75c39d97241f3391. Report an issue: GitHub.