microsoft/garnet · error · ArgumentException

Elements collection cannot be empty.

Error message

Elements collection cannot be empty.

What it means

ListLeftPush(key, IEnumerable<string> elements, ...) builds arrElem = {key} ∪ elements and throws ArgumentException when the union has length 1 — meaning elements contributed zero items. This rejects an empty LPUSH (Redis semantics: LPUSH requires at least one value). The key-only array is detected as the degenerate case.

Source

Thrown at libs/client/GarnetClientAPI/GarnetClientListCommands.cs:47

        /// <summary>
        /// Add the specified elements to the head of the list stored at key.
        /// </summary>
        /// <param name="key">The key of the list.</param>
        /// <param name="elements">The elements to be added.</param>
        /// <param name="callback">The callback function when operation completes.</param>
        /// <param name="context">An optional context to correlate request to callback.</param>
        public void ListLeftPush(string key, IEnumerable<string> elements, Action<long, long, string> callback, long context = 0)
        {
            ArgumentNullException.ThrowIfNull(key);
            ArgumentNullException.ThrowIfNull(elements);
            ArgumentNullException.ThrowIfNull(callback);

            var arrElem = new[] { key }.Union(elements).ToArray();

            if (arrElem.Length == 1)
            {
                throw new ArgumentException("Elements collection cannot be empty.", nameof(elements));
            }

            ExecuteForLongResult(callback, context, nameof(LPUSH), arrElem);
        }

        /// <summary>
        /// Asynchronously add the specified elements to the head of the list stored at key.
        /// </summary>
        /// <param name="key">The key of the list.</param>
        /// <param name="elements">The elements to be added.</param>
        /// <returns>The number of list elements after the addition.</returns>
        public async Task<long> ListLeftPushAsync(string key, params string[] elements)
        {
            ArgumentNullException.ThrowIfNull(key);
            ArgumentNullException.ThrowIfNull(elements);

            if (elements.Length == 0)
            {

View on GitHub (pinned to 951b0fc683)

Solutions

1. Check elements.Any() before calling ListLeftPush, or skip the call entirely when there is nothing to push.
2. Use the async ListLeftPushAsync(params string[]) overload only if you have at least one element.
3. Guard the caller to never construct an empty push.

Example fix

// before
client.ListLeftPush(key, values, callback);

// after — skip empty pushes
if (values is null || !values.Any()) return;
client.ListLeftPush(key, values, callback);

if (elements is null || !elements.Any()) return; // or throw a clearer error at the caller
client.ListLeftPush(key, elements, callback);

bool HasElements(IEnumerable<string> e) => e is not null && e.Any();

When it happens

Trigger: Calling ListLeftPush with an empty IEnumerable<string>, or one whose Union with {key} yields only the key (e.g. elements is an empty list, or contains only items already equal to key that get de-duplicated by Union).

Common situations: Passing an empty collection variable (e.g. from a query that returned no rows); a default/empty List<string>; a code path that pushes only when data exists but the guard is missing.

Related errors

• Failed to connect at {EndPoint}
• Invalid ClusterConfig payload: too short to contain a versio
• Gossip sample fraction should be in range [0,100]
• Azure Storage connection string is required to read/write to
• Assembly is required to read from embedded resource

AI-assisted analysis of microsoft/garnet@951b0fc683 (2026-08-13). Data as JSON: /api/errors/90f0cd7929cd1d4d. Report an issue: GitHub.