What causes "other" in cefsharp/CefSharp?

Ensure the source IRequestContext is created first (e.g. obtain it from an existing ChromiumWebbrowser.GetRequestContext() or Cef.GetGlobalRequestContext()).

cefsharp/CefSharp · error · ArgumentNullException

other

Error message

other

What it means

ArgumentNullException("other") from RequestContextBuilder.WithSharedSettings(IRequestContext other). Sharing storage requires a source context; passing null is meaningless so it fails fast with parameter name 'other' (note: hardcoded string, not nameof). This check runs before ThrowExceptionIfCustomSettingSpecified.

Solutions

Ensure the source IRequestContext is created first (e.g. obtain it from an existing ChromiumWebbrowser.GetRequestContext() or Cef.GetGlobalRequestContext()).
Guard the call: only invoke WithSharedSettings when the source is non-null, otherwise fall back to a custom-settings builder.
Register IRequestContext as a non-null singleton in DI.
Enable nullable reference types to catch the null statically.

Example fix

// before
var ctx = RequestContext.Configure().WithSharedSettings(parent).Create(); // parent null -> throws

// after
var parent = existingBrowser?.GetRequestContext();
var builder = RequestContext.Configure();
if (parent != null) builder = builder.WithSharedSettings(parent);
else builder = builder.WithCachePath(@"C:\cache");
var ctx = builder.Create();

Defensive patterns

Strategy: validation

Validate before calling

if (parent == null) throw new InvalidOperationException("No RequestContext to share.");
var ctx = RequestContext.Configure().WithSharedSettings(parent).Create();

Type guard

public static bool IsShareable(IRequestContext c) => c != null;

Try / catch

try { return RequestContext.Configure().WithSharedSettings(parent).Create(); }
catch (ArgumentNullException ex) when (ex.ParamName == "other")
{ /* fall back to custom settings */ return RequestContext.Configure().WithCachePath(cache).Create(); }

Prevention

Create/obtain the parent IRequestContext before sharing
Register IRequestContext as a non-null singleton in DI
Enable nullable reference types

When it happens

Trigger: Calling .WithSharedSettings(null) or .WithSharedSettings(unassignedVariable); passing an IRequestContext obtained from a browser that is not yet created; DI resolving IRequestContext to null.

Common situations: Trying to share the global context before it exists; factory returning null; overload/dispose race where the source context was just disposed.

Related errors

AI-assisted analysis of cefsharp/CefSharp@16bc6e0711 (2026-08-13). Data as JSON: /api/errors/5b4b0520d16ac912. Report an issue: GitHub.

Appendix: source

Thrown at CefSharp.Core/RequestContextBuilder.cs:202

            {
                _handler = new RequestContextHandler();
            }

            _handler.SetProxyOnContextInitialized(scheme, host, port);

            return this;
        }

        /// <summary>
        /// Shares storage with other RequestContext
        /// </summary>
        /// <param name="other">shares storage with this RequestContext</param>
        /// <returns>Returns RequestContextBuilder instance</returns>
        public RequestContextBuilder WithSharedSettings(IRequestContext other)
        {
            if (other == null)
            {
                throw new ArgumentNullException("other");
            }

            ThrowExceptionIfCustomSettingSpecified();

            _otherContext = other;

            return this;
        }
    }
}

View on GitHub (pinned to 16bc6e0711)