cefsharp/CefSharp · error · ArgumentNullException

requestContextHandler

Error message

requestContextHandler

What it means

ArgumentNullException(nameof(requestContextHandler)) from the two-argument RequestContext(IRequestContext otherRequestContext, IRequestContextHandler requestContextHandler) constructor - the second guard. The parent passed the first check, but the handler is null, which is invalid for this overload because it explicitly pairs a shared context with a handler.

Source

Thrown at CefSharp.Core/RequestContext.cs:45

        {
            if (otherRequestContext == null)
            {
                throw new ArgumentNullException(nameof(otherRequestContext));
            }
            requestContext = new CefSharp.Core.RequestContext(otherRequestContext);
        }

        /// <inheritdoc/>
        public RequestContext(IRequestContext otherRequestContext, IRequestContextHandler requestContextHandler)
        {
            if (otherRequestContext == null)
            {
                throw new ArgumentNullException(nameof(otherRequestContext));
            }

            if (requestContextHandler == null)
            {
                throw new ArgumentNullException(nameof(requestContextHandler));
            }

            requestContext = new CefSharp.Core.RequestContext(otherRequestContext, requestContextHandler);
        }

        /// <inheritdoc/>
        public RequestContext(IRequestContextHandler requestContextHandler)
        {
            if (requestContextHandler == null)
            {
                throw new ArgumentNullException(nameof(requestContextHandler));
            }
            requestContext = new CefSharp.Core.RequestContext(requestContextHandler);
        }

        /// <inheritdoc/>
        public RequestContext(RequestContextSettings settings)
        {

View on GitHub (pinned to 16bc6e0711)

Solutions

1. Provide a real IRequestContextHandler implementation; if you do not need hooks, use the single-argument RequestContext(parent) overload instead.
2. If you only need lifecycle hooks conditionally, branch: pick the overload based on whether a handler exists.
3. Use RequestContextBuilder to fluently attach only the handlers you need without passing null.
4. Enable nullable reference types to surface the null at compile time.

Example fix

// before
var ctx = new RequestContext(parent, null); // throws

// after - pick the overload that matches intent
var ctx = handler == null ? new RequestContext(parent) : new RequestContext(parent, handler);

// If no handler is needed, use the single-arg overload.
var ctx = handler == null ? new RequestContext(parent) : new RequestContext(parent, handler);

public static bool HasHandler(IRequestContextHandler h) => h != null;

try { return new RequestContext(parent, handler); }
catch (ArgumentNullException ex) when (ex.ParamName == "requestContextHandler")
{ return new RequestContext(parent); }

When it happens

Trigger: Calling new RequestContext(parent, null) intending 'no handler'; passing a handler field that was never assigned; DI resolving IRequestContextHandler to null.

Common situations: Assuming the handler is optional in this overload (it is not); reusing a builder that conditionally produces a handler and produces null in the no-op branch.

Related errors

• otherRequestContext
• settings
• other
• request
• {prop.Name} is required

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/a1f800010cc01bbd. Report an issue: GitHub.