RicoSuter/NSwag · error · ArgumentNullException

key

Error message

key

What it means

ObservableDictionary.Remove throws ArgumentNullException when the key argument is null. Null is never a valid dictionary key here, so the method fails fast before attempting the underlying Dictionary.Remove and collection-change notification.

Solutions

1. Ensure the key variable is non-null before calling Remove
2. Check ContainsKey with a non-null key first; skip removal if null
3. Use an early return: if (key == null) return false;

Example fix

// before
dict.Remove(key);
// after
if (key != null && dict.ContainsKey(key))
{
    dict.Remove(key);
}

if (key != null) dict.Remove(key);

bool canRemove = key is not null;

When it happens

Trigger: Calling Remove(null) on an ObservableDictionary, e.g. removing a schema or parameter keyed by a variable that was never assigned.

Common situations: Removing an OpenAPI component by a name that came from optional config or a failed lookup that returned null.

Related errors

• items
• An item with the same key has already been added.
• document
• globalScopeNames
• This UI does not support multiple documents per UI: Do not…

AI-assisted analysis of RicoSuter/NSwag@63daf8fcc3 (2026-09-14). Data as JSON: /api/errors/a544e0f84f5aff68. Report an issue: GitHub.

Appendix: source

Thrown at src/NSwag.Core/Collections/ObservableDictionary.cs:217

        public ICollection<TKey> Keys => _dictionary.Keys;

        internal Dictionary<TKey, TValue>.KeyCollection KeyCollection => _dictionary.Keys;

        ICollection IDictionary.Values => _dictionary.Values;

        ICollection IDictionary.Keys => _dictionary.Keys;

        IEnumerable<TValue> IReadOnlyDictionary<TKey, TValue>.Values => Values;

        /// <summary>Removes the specified key.</summary>
        /// <param name="key">The key.</param>
        /// <returns></returns>
        /// <exception cref="System.ArgumentNullException">key</exception>
        public virtual bool Remove(TKey key)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            var removed = _dictionary.Remove(key);
            if (removed)
            {
                OnCollectionChanged();
            }
            //OnCollectionChanged(NotifyCollectionChangedAction.Remove, new KeyValuePair<TKey, TValue>(key, value));
            return removed;
        }

        /// <summary>Tries the get value.</summary>
        /// <param name="key">The key.</param>
        /// <param name="value">The value.</param>
        /// <returns></returns>
        public bool TryGetValue(TKey key, out TValue value)
        {
            return _dictionary.TryGetValue(key, out value);

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