alibaba/nacos · warning · IllegalArgumentException

Unsupported object type: null

Error message

Unsupported object type: null

What it means

Thrown by CollectionUtils.sizeIsEmpty(Object) when the argument is null. Unlike most 'isEmpty' helpers, this method deliberately rejects null instead of treating it as empty — passing null is treated as a programming error, not an empty collection.

Source

Thrown at common/src/main/java/com/alibaba/nacos/common/utils/CollectionUtils.java:196

     * Judge whether object is empty.
     *
     * @param object object
     * @return true if object is empty, otherwise false
     * @throws IllegalArgumentException if object has no length or size
     */
    public static boolean sizeIsEmpty(Object object) {
        if (object instanceof Collection) {
            return ((Collection) object).isEmpty();
        } else if (object instanceof Map) {
            return ((Map) object).isEmpty();
        } else if (object instanceof Object[]) {
            return ((Object[]) object).length == 0;
        } else if (object instanceof Iterator) {
            return ((Iterator) object).hasNext() == false;
        } else if (object instanceof Enumeration) {
            return ((Enumeration) object).hasMoreElements() == false;
        } else if (object == null) {
            throw new IllegalArgumentException("Unsupported object type: null");
        } else {
            try {
                return Array.getLength(object) == 0;
            } catch (IllegalArgumentException ex) {
                throw new IllegalArgumentException(
                    "Unsupported object type: " + object.getClass().getName());
            }
        }
    }
    
    /**
     * Whether contain item in collection.
     *
     * @param coll   collection
     * @param target target value
     * @param <T>    General Type
     * @return true if contain, otherwise false
     */

View on GitHub (pinned to 9b989acdf1)

Solutions

1. Null-check before calling: if (obj != null && sizeIsEmpty(obj)) ...
2. Prefer CollectionUtils.isEmpty(coll) / isNotEmpty(coll) for null-safe behavior when you only deal with Collections.
3. Fix the upstream null return so the invariant the method assumes holds.

Example fix

// before
boolean empty = CollectionUtils.sizeIsEmpty(maybeNull);

// after
boolean empty = maybeNull != null && CollectionUtils.sizeIsEmpty(maybeNull);

if (object == null) {
    // treat as empty or reject explicitly — sizeIsEmpty will not accept null
    return; // or throw a domain error
}
boolean empty = CollectionUtils.sizeIsEmpty(object);

boolean isSizeable(Object o) {
    return o instanceof Collection || o instanceof Map
        || o instanceof Object[] || o instanceof Iterator
        || o instanceof Enumeration;
}

When it happens

Trigger: Calling CollectionUtils.sizeIsEmpty(null). Any caller that passes an unguarded null variable hits this immediately.

Common situations: A nullable field or method result passed into sizeIsEmpty without a null check; refactoring that introduced a nullable return upstream.

Related errors

• iterable cannot be null.
• Unsupported object type: {}
• Expected an array of elements (or empty array) but received
• expected one element but was: <{}>
• Agent replacement must not be null

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/d16d89520c4f26b4. Report an issue: GitHub.