cefsharp/CefSharp · error · ArgumentNullException

manager

Error message

manager

What it means

Thrown by the CookieManagerDecorator constructor when the inner ICookieManager passed to it is null. CookieManagerDecorator wraps a real cookie manager and guards access until the underlying CEF cookie store is ready; without a wrapped instance there is nothing to delegate to. The decorator is created internally by CefSharp when providing the per-request-context cookie manager.

Source

Thrown at CefSharp/Internals/CookieManagerDecorator.cs:24

using System.Threading.Tasks;

namespace CefSharp.Internals
{
    /// <summary>
    /// CookieManager with additional checks to ensure the store is initialized.
    /// Throws an exception when attempting to access the store before it's ready.
    /// </summary>
    public class CookieManagerDecorator : ICookieManager
    {
        private const string NotInitialziedExceptionMsg = "CookieManager store is not initialized.";
        private ICookieManager manager;
        private volatile bool managerReady;

        internal CookieManagerDecorator(ICookieManager manager, TaskCompletionCallback callback)
        {
            if (manager == null)
            {
                throw new ArgumentNullException("manager");
            }
            if (callback == null)
            {
                throw new ArgumentNullException("manager");
            }

            this.manager = manager;

            if (callback.Task.Status == TaskStatus.RanToCompletion)
            {
                managerReady = callback.Task.Result;
            }
            else
            {
                callback.Task.ContinueWith(x =>
                {
                    managerReady = x.Result;
                });

View on GitHub (pinned to 16bc6e0711)

Solutions

1. Ensure the ICookieManager instance supplied is non-null; if you obtained it from RequestContext.GetCookieManager, verify the request context is valid and initialized.
2. If extending/wrapping CefSharp internals, validate the manager reference before constructing the decorator.
3. Check for a CefSharp version mismatch or broken custom factory that yields null managers.

Example fix

// before
var decorator = new CookieManagerDecorator(manager, callback);

// after
if (manager == null) throw new InvalidOperationException("Cookie manager must be created first.");
var decorator = new CookieManagerDecorator(manager, callback);

if (manager == null)
{
    throw new InvalidOperationException("Inner cookie manager is not available; create the request context first.");
}
// internal ctor — only construct through the official CefSharp path

When it happens

Trigger: Internal construction of CookieManagerDecorator with a null manager argument. As an internal ctor this is normally invoked by CefSharp internals (e.g. RequestContext.GetCookieManager path); a null indicates an upstream wiring bug or a custom subclass/factory producing a null manager.

Common situations: Custom RequestContext/cookie-manager integration that constructs or reflects over CookieManagerDecorator incorrectly; version mismatch where an internal contract changed; a null returned from a custom ICookieManager provider being passed through.

Related errors

• Please provide a valid array
• Please provide a valid filePath
• Please provide a valid mimeType
• Unable to load byte[] with length 0.
• converter

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/082f7c061b5994a7. Report an issue: GitHub.