dotnet/maui · error · InvalidOperationException

The property {0} cannot be null at this time.

Error message

The property {0} cannot be null at this time.

What it means

Verify.PropertyIsNotNull<T> (where T : class) throws InvalidOperationException (not ArgumentException) when the property value is null. Unlike the argument guards, this is a state guard — it signals that the object's current state is invalid because a required property has not been set. The message is formatted with the property name.

Source

Thrown at src/Compatibility/Core/src/WPF/Microsoft.Windows.Shell/Standard/Verify.cs:150

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void IsNull<T>(T obj, string name) where T : class
		{
			if (null != obj)
			{
				Assert.Fail();
				throw new ArgumentException("The parameter must be null.", name);
			}
		}

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void PropertyIsNotNull<T>(T obj, string name) where T : class
		{
			if (null == obj)
			{
				Assert.Fail();
				throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, "The property {0} cannot be null at this time.", name));
			}
		}

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[DebuggerStepThrough]
		public static void PropertyIsNull<T>(T obj, string name) where T : class
		{
			if (null != obj)
			{
				Assert.Fail();
				throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, "The property {0} must be null at this time.", name));
			}
		}

		/// <summary>
		/// Verifies the specified statement is true.  Throws an ArgumentException if it's not.
		/// </summary>
		/// <param name="statement">The statement to be verified as true.</param>

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Set the required property before invoking the operation that depends on it.
2. Verify initialization order — ensure all required properties are assigned in the constructor or init path.
3. Add a state check in your own code (if (obj.Property == null) throw) earlier with a clearer message.

Example fix

// before
chromeWindow.ApplyChrome();

// after
if (chromeWindow.ChromeInfo == null)
{
    throw new InvalidOperationException("ChromeInfo must be set before applying.");
}
chromeWindow.ApplyChrome();

// Pre-check: required property must be set before the operation
if (obj.RequiredProperty == null)
{
    throw new InvalidOperationException("RequiredProperty must be set before this operation.");
}
obj.DoOperation();

try
{
    obj.DoOperation();
}
catch (InvalidOperationException ex) when (ex.Message.Contains("cannot be null"))
{
    // log and guide the user to set required properties
    throw;
}

When it happens

Trigger: Calling a method that internally asserts Verify.PropertyIsNotNull(_someProperty, "SomeProperty") before the property has been assigned. The guard fires because a precondition on internal state was violated.

Common situations: Using an object before its required properties are set (e.g. calling Show before Title is assigned); a dependency property or service was never injected; initialization ran partially and a setter was skipped.

Related errors

• The property {0} must be null at this time.
• The parameter cannot be either null or empty.
• The parameter cannot be either null or empty or consist only
• The parameter must not be the default value.
• The parameter must be null.

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/f7bbb42e426ccb61. Report an issue: GitHub.