apache/flink · error · IllegalArgumentException

The input {} contains an empty argument

Error message

The input {} contains an empty argument

What it means

ParameterTool.fromArgs walks the args array expecting '--key value' pairs; after stripping leading dashes an argument that is empty (the empty string, or a bare '-'/'--') yields an empty key and this IllegalArgumentException printing the whole args array. It is a fail-fast check that the CLI contract (non-empty flag names) is met.

Source

Thrown at flink-core/src/main/java/org/apache/flink/util/ParameterTool.java:70

    /**
     * Returns {@link ParameterTool} for the given arguments. The arguments are keys followed by
     * values. Keys have to start with '-' or '--'
     *
     * <p><strong>Example arguments:</strong> --key1 value1 --key2 value2 -key3 value3
     *
     * @param args Input array arguments
     * @return A {@link ParameterTool}
     */
    public static ParameterTool fromArgs(String[] args) {
        final Map<String, String> map = CollectionUtil.newHashMapWithExpectedSize(args.length / 2);

        int i = 0;
        while (i < args.length) {
            final String key = Utils.getKeyFromArgs(args, i);

            if (key.isEmpty()) {
                throw new IllegalArgumentException(
                        "The input " + Arrays.toString(args) + " contains an empty argument");
            }

            i += 1; // try to find the value

            if (i >= args.length) {
                map.put(key, AbstractParameterTool.NO_VALUE_KEY);
            } else if (NumberUtils.isNumber(args[i])) {
                map.put(key, args[i]);
                i += 1;
            } else if (args[i].startsWith("--") || args[i].startsWith("-")) {
                // the argument cannot be a negative number because we checked earlier
                // -> the next argument is a parameter name
                map.put(key, AbstractParameterTool.NO_VALUE_KEY);
            } else {
                map.put(key, args[i]);
                i += 1;
            }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Inspect the printed args array to find the empty element and remove it.
2. Fix the launcher: filter empty strings before calling Flink, e.g. Arrays.stream(args).filter(s -> !s.isEmpty()).
3. In shell scripts, quote variables and guard optional flags so empty values are not passed at all.

Example fix

// before
ParameterTool params = ParameterTool.fromArgs(args); // args contains ""

// after
String[] cleaned = Arrays.stream(args).filter(s -> !s.isEmpty()).toArray(String[]::new);
ParameterTool params = ParameterTool.fromArgs(cleaned);

String[] cleaned = Arrays.stream(args).filter(s -> s != null && !s.isEmpty() && !s.equals("--") && !s.equals("-")).toArray(String[]::new);
ParameterTool params = ParameterTool.fromArgs(cleaned);

When it happens

Trigger: args containing "" (e.g. from a shell quoting bug), a lone "--" or "-" used as a separator, or an option name reduced to nothing after '--' stripping.

Common situations: Shell scripts passing "$EMPTY_VAR" unquoted-expanded; argument lists built by joining with stray empty elements; users inserting '--' expecting an end-of-options marker.

Related errors

• Value for config option %s must be one of %s (was %s)
• Segment size must be a power of 2!
• {directory} is not a directory but a regular file
• Invalid port configuration. Port must be between 0and 65535,
• Invalid port configuration. Port must be between 0and 65535,

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/ea0aca4ff903c1ef. Report an issue: GitHub.