apache/flink · error · NullPointerException

address is null

Error message

address is null

What it means

NetUtils.ipAddressToUrlString explicitly rejects a null InetAddress with a NullPointerException carrying the message 'address is null'. Only Inet4Address and Inet6Address are handled afterwards. It fires when callers pass an address that was never resolved or a field that was never set.

Source

Thrown at flink-core/src/main/java/org/apache/flink/util/NetUtils.java:279

     * @param host The hostname, IPv4 or IPv6 address
     * @param port The port
     * @return host:port where host will be normalized if it is an IPv6 address
     */
    public static String unresolvedHostAndPortToNormalizedString(String host, int port) {
        Preconditions.checkArgument(isValidHostPort(port), "Port is not within the valid range,");
        return unresolvedHostToNormalizedString(host) + ":" + port;
    }

    /**
     * Encodes an IP address properly as a URL string. This method makes sure that IPv6 addresses
     * have the proper formatting to be included in URLs.
     *
     * @param address The IP address to encode.
     * @return The proper URL string encoded IP address.
     */
    public static String ipAddressToUrlString(InetAddress address) {
        if (address == null) {
            throw new NullPointerException("address is null");
        } else if (address instanceof Inet4Address) {
            return address.getHostAddress();
        } else if (address instanceof Inet6Address) {
            return getIPv6UrlRepresentation((Inet6Address) address);
        } else {
            throw new IllegalArgumentException("Unrecognized type of InetAddress: " + address);
        }
    }

    /**
     * Encodes an IP address and port to be included in URL. in particular, this method makes sure
     * that IPv6 addresses have the proper formatting to be included in URLs.
     *
     * @param address The address to be included in the URL.
     * @param port The port for the URL address.
     * @return The proper URL string encoded IP address and port.
     */
    public static String ipAddressAndPortToUrlString(InetAddress address, int port) {

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Find who passes null: usually a DNS/lookup step whose failure path returned null instead of throwing.
2. Resolve the address before calling, or skip URL construction when the address is absent.
3. Prefer InetSocketAddress-based APIs (socketAddressToUrlString) if you have host+port, keeping the null/resolve check in one place.

Example fix

// before
String url = NetUtils.ipAddressToUrlString(lookupHost(host)); // returns null on failure

// after
InetAddress addr = Objects.requireNonNull(lookupHost(host), "host not resolved: " + host);
String url = NetUtils.ipAddressToUrlString(addr);

InetAddress addr = Objects.requireNonNull(address, "address must be resolved before URL conversion");
String url = NetUtils.ipAddressToUrlString(addr);

if (address == null) { throw new IllegalStateException("address not resolved for " + host); } // fail before calling the API instead of catching NPE

When it happens

Trigger: Calling NetUtils.ipAddressToUrlString(null) or ipAddressAndPortToUrlString(null, port); passing an InetAddress obtained from a failed lookup helper that returns null on error.

Common situations: glue code that maps 'lookup failed' to null; constructing URLs for a service whose address field is optional and unset; refactors that drop the resolution step.

Related errors

• Id must not be null.
• The given host:port ('{}') doesn't contain a valid host
• The given host:port ('{}') doesn't contain a valid port
• The given host:port ('{}') is invalid
• Could not find a free permitted port on the machine.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/0980e591f98efdbc. Report an issue: GitHub.