didi/DoKit · error · IllegalArgumentException

comparator must not be null

Error message

comparator must not be null

What it means

MapUtils.newTreeMap(comparator, pairs...) builds a TreeMap keyed by the supplied Comparator because a TreeMap without a natural ordering needs one. Passing null would make the TreeMap constructor itself throw NullPointerException later, so the utility fails fast with IllegalArgumentException('comparator must not be null').

Source

Thrown at Android/dokit-util/src/main/java/com/didichuxing/doraemonkit/util/MapUtils.java:69

    @SafeVarargs
    public static <K, V> LinkedHashMap<K, V> newLinkedHashMap(final Pair<K, V>... pairs) {
        LinkedHashMap<K, V> map = new LinkedHashMap<>();
        if (pairs == null || pairs.length == 0) {
            return map;
        }
        for (Pair<K, V> pair : pairs) {
            if (pair == null) continue;
            map.put(pair.first, pair.second);
        }
        return map;
    }

    @SafeVarargs
    public static <K, V> TreeMap<K, V> newTreeMap(final Comparator<K> comparator,
                                                  final Pair<K, V>... pairs) {
        if (comparator == null) {
            throw new IllegalArgumentException("comparator must not be null");
        }
        TreeMap<K, V> map = new TreeMap<>(comparator);
        if (pairs == null || pairs.length == 0) {
            return map;
        }
        for (Pair<K, V> pair : pairs) {
            if (pair == null) continue;
            map.put(pair.first, pair.second);
        }
        return map;
    }

    @SafeVarargs
    public static <K, V> Hashtable<K, V> newHashTable(final Pair<K, V>... pairs) {
        Hashtable<K, V> map = new Hashtable<>();
        if (pairs == null || pairs.length == 0) {
            return map;
        }

View on GitHub (pinned to 626827cddb)

Solutions

1. Pass a real comparator, e.g. naturalOrder(): newTreeMap(Comparator.<K>naturalOrder(), pairs...).
2. If null was meant as 'no sorting', use HashMapUtils-style newHashMap/newLinkedHashMap instead.
3. When comparator choice is dynamic, default it: comparator != null ? comparator : Comparator.naturalOrder().

Example fix

// before
TreeMap<String, Integer> m = MapUtils.newTreeMap(null, p1, p2); // throws

// after
TreeMap<String, Integer> m = MapUtils.newTreeMap(Comparator.<String>naturalOrder(), p1, p2);

Comparator<K> cmp = comparator != null ? comparator : Comparator.<K>naturalOrder();
TreeMap<K, V> m = MapUtils.newTreeMap(cmp, pairs);

When it happens

Trigger: Calling newTreeMap(null, pair1, pair2), typically from Kotlin where the comparator parameter has no default, or from Java passing a conditionally-created comparator that evaluated to null.

Common situations: Optional-sorting code that builds a comparator only when a sort field is configured; DI/injection returning null for a comparator dependency; copy-paste from newHashMap usage where null args were tolerated.

Related errors

• Transformation list must not be null.
• Index cannot be negative: " + index
• Entry does not exist: " + index
• Unsupported object type: " + object.getClass().getName()
• field == null

AI-assisted analysis of didi/DoKit@626827cddb (2026-08-14). Data as JSON: /api/errors/70333863fbbbcbbb. Report an issue: GitHub.