dotnet/maui · error · ArgumentException

The parameter must not be the default value.

Error message

The parameter must not be the default value.

What it means

Verify.IsNotDefault<T> (where T : struct) throws ArgumentException when obj.Equals(default(T)) — i.e. the value is the zero/default representation of its value type. This guard is used to reject uninitialized structs (Guid.Empty, default IntPtr, IntPtr.Zero, etc.).

Source

Thrown at src/Compatibility/Core/src/WPF/Microsoft.Windows.Shell/Standard/Verify.cs:109

			if ("" == value.Trim())
			{
				Assert.Fail();
				throw new ArgumentException(errorMessage, name);
			}
		}

		/// <summary>Verifies that an argument is not null.</summary>
		/// <typeparam name="T">Type of the object to validate.  Must be a class.</typeparam>
		/// <param name="obj">The object to validate.</param>
		/// <param name="name">The name of the parameter that will be presented if an exception is thrown.</param>
		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void IsNotDefault<T>(T obj, string name) where T : struct
		{
			if (default(T).Equals(obj))
			{
				Assert.Fail();
				throw new ArgumentException("The parameter must not be the default value.", name);
			}
		}

		/// <summary>Verifies that an argument is not null.</summary>
		/// <typeparam name="T">Type of the object to validate.  Must be a class.</typeparam>
		/// <param name="obj">The object to validate.</param>
		/// <param name="name">The name of the parameter that will be presented if an exception is thrown.</param>
		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void IsNotNull<T>(T obj, string name) where T : class
		{
			if (null == obj)
			{
				Assert.Fail();
				throw new ArgumentNullException(name);
			}
		}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Initialize the struct to a meaningful non-default value before the call.
2. If the value comes from a lookup, check for default(T) before forwarding (e.g. if (handle == IntPtr.Zero)).
3. Use nullable wrappers (Guid?) when absence is a valid state.

Example fix

// before
Register(id); // id may be Guid.Empty

// after
if (id == Guid.Empty)
{
    throw new ArgumentException("A valid id is required.", nameof(id));
}
Register(id);

// Pre-check for default value-type before calling the guarded API
if (value.Equals(default(T)))
{
    throw new ArgumentException($"Value must not be the default {typeof(T).Name}.", nameof(value));
}
SomeApi(value);

When it happens

Trigger: Calling a method guarded by Verify.IsNotDefault(value, name) where value is default(T) for its struct type — e.g. Guid.Empty, new IntPtr(0), default(DateTime), or a zero-valued handle struct.

Common situations: A Guid was never assigned and left as Guid.Empty; an IntPtr handle was not obtained from the OS; a value-type enum defaulted to 0 which is not a valid member; a struct field was declared but never initialized.

Related errors

• The parameter cannot be either null or empty.
• The parameter cannot be either null or empty or consist only
• The parameter must be null.
• The URI must be absolute.
• The integer value must be bounded with [{0}, {1})

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/ecf14b3e495a784b. Report an issue: GitHub.