alibaba/nacos · warning · IllegalArgumentException

Unsupported object type: {}

Error message

Unsupported object type: {}

What it means

Thrown by CollectionUtils.sizeIsEmpty(Object) when the argument is a non-null object that is not a Collection, Map, Object[], Iterator, or Enumeration, and Array.getLength(object) also throws. The message appends the actual class name so you can see what was passed.

Source

Thrown at common/src/main/java/com/alibaba/nacos/common/utils/CollectionUtils.java:201

     */
    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
     */
    public static <T> boolean contains(Collection<T> coll, T target) {
        if (isEmpty(coll)) {
            return false;
        }
        return coll.contains(target);

View on GitHub (pinned to 9b989acdf1)

Solutions

1. Check the class name in the error message to confirm what was passed.
2. Convert the input to a supported type before calling (e.g., Arrays.asList for arrays, wrap in a collection).
3. For Strings use str.isEmpty(); for primitive arrays use array.length directly.

Example fix

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

// after
boolean empty = someString == null || someString.isEmpty();

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

try {
    return CollectionUtils.sizeIsEmpty(obj);
} catch (IllegalArgumentException e) {
    // obj was a String, primitive array, or arbitrary POJO
    return false; // or compute size the type-specific way
}

When it happens

Trigger: Calling sizeIsEmpty with an arbitrary object such as a String, a primitive array (int[]), a custom POJO, or any type without a measurable size.

Common situations: Passing a String (common mistake — length is queried differently); passing a primitive array like int[] (only Object[] is supported); passing a POJO where a Collection was expected.

Related errors

• Unsupported object type: null
• iterable cannot be null.
• expected one element but was: <{}>
• Agent Version storage {field} must be a string
• Agent Version storage {field} must be an integer

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/e1be199cb3dfdad0. Report an issue: GitHub.