JamesNK/Newtonsoft.Json · error · ArgumentNullException

array

Error message

array

What it means

CopyItemsTo (which backs CopyTo) throws ArgumentNullException named 'array' when the destination array is null. The null-array guard runs before any bounds checks.

Source

Thrown at Src/Newtonsoft.Json/Linq/JContainer.cs:593

            if (existing == null || existing.Parent != this)
            {
                return;
            }

            int index = IndexOfItem(existing);
            SetItem(index, replacement);
        }

        internal virtual bool ContainsItem(JToken? item)
        {
            return (IndexOfItem(item) != -1);
        }

        internal virtual void CopyItemsTo(Array array, int arrayIndex)
        {
            if (array == null)
            {
                throw new ArgumentNullException(nameof(array));
            }
            if (arrayIndex < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(arrayIndex), "arrayIndex is less than 0.");
            }
            if (arrayIndex >= array.Length && arrayIndex != 0)
            {
                throw new ArgumentException("arrayIndex is equal to or greater than the length of array.");
            }
            if (Count > array.Length - arrayIndex)
            {
                throw new ArgumentException("The number of elements in the source JObject is greater than the available space from arrayIndex to the end of the destination array.");
            }

            int index = 0;
            foreach (JToken token in ChildrenTokens)
            {
                array.SetValue(token, arrayIndex + index);

View on GitHub (pinned to 4f73e74372)

Solutions

1. Allocate the destination array before copying: new JToken[container.Count].
2. Null-check the array argument at the call site and fail with a clear message.
3. Use the ToList()/LINQ materialization if you just need a snapshot.

Example fix

// before
arr.CopyTo(null, 0);
// after
var dest = new JToken[arr.Count];
arr.CopyTo(dest, 0);

var dest = array ?? new JToken[container.Count];
container.CopyTo(dest, 0);

try { container.CopyTo(dest, arrayIndex); }
catch (ArgumentNullException ex) when (ex.ParamName == "array") {
    dest = new JToken[container.Count];
    container.CopyTo(dest, 0);
}

When it happens

Trigger: jArray.CopyTo(null, 0); ((ICollection)container).CopyTo(null, 0); passing a null array variable.

Common situations: Uninitialized destination array; generic collection-copy helper that forwards a null.

Related errors

• arrayIndex is less than 0.
• arrayIndex is equal to or greater than the length of array.
• The number of elements in the source JObject is greater than
• Index must be within the bounds of the List.
• Index is less than 0.

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/0477cdf2a5e7fa17. Report an issue: GitHub.