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.

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

• A REST Client Response object was returned from a server…
• A REST Client RestResponse object was returned from a…
• Invalid port number
• Invalid port number
• Invalid proxy setting. The port is not a number in

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

Appendix: 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;

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