What causes "page" in dotnet/maui?

Null-check the page before calling PushModalAsync

dotnet/maui · error · ArgumentNullException

page

Error message

page

What it means

PushModalAsync on the Windows Platform INavigation throws ArgumentNullException when the page parameter is null. The guard is a simple null check before adding the page to the navigation model via _navModel.PushModal.

Source

Thrown at src/Compatibility/Core/src/Windows/Platform.cs:250

		{
			throw new InvalidOperationException(
				"InsertPageBefore is not supported globally on Windows, please use a NavigationPage.");
		}

		Task INavigation.PushModalAsync(Page page)
		{
			return ((INavigation)this).PushModalAsync(page, true);
		}

		Task<Page> INavigation.PopModalAsync()
		{
			return ((INavigation)this).PopModalAsync(true);
		}

		Task INavigation.PushModalAsync(Page page, bool animated)
		{
			if (page == null)
				throw new ArgumentNullException(nameof(page));

			var tcs = new TaskCompletionSource<bool>();
			_navModel.PushModal(page);
			SetCurrent(page, false, true, () => tcs.SetResult(true));
			return tcs.Task;
		}

		Task<Page> INavigation.PopModalAsync(bool animated)
		{
			var tcs = new TaskCompletionSource<Page>();
			Page result = _navModel.PopModal();
			SetCurrent(_navModel.CurrentPage, true, true, () => tcs.SetResult(result));
			return tcs.Task;
		}

		public static SizeRequest GetNativeSize(VisualElement element, double widthConstraint, double heightConstraint)
		{
			// Hack around the fact that Canvas ignores the child constraints.

View on GitHub (pinned to f377ff1c5e)

Solutions

Null-check the page before calling PushModalAsync
Ensure the page factory or resolver always returns a valid Page instance
Use a guard clause: if (page == null) return;

Example fix

// before
await Navigation.PushModalAsync(resolvedPage); // throws if resolvedPage is null

// after
if (resolvedPage == null)
    throw new InvalidOperationException("Page could not be resolved");
await Navigation.PushModalAsync(resolvedPage);

Defensive patterns

Strategy: validation

Validate before calling

// Before calling PushModalAsync, null-check the page
if (page == null)
    throw new ArgumentNullException(nameof(page), "Cannot push a null page modally");
await Navigation.PushModalAsync(page);

Prevention

Always null-check page references before navigation calls
Ensure page factories/resolvers return valid instances or throw early
Use guard clauses at the top of navigation methods

When it happens

Trigger: Calling Navigation.PushModalAsync(null) or passing a variable that evaluates to null at runtime, such as a factory method result or a deserialized page reference.

Common situations: Page factory or resolver returns null under certain conditions; conditional page construction where the page wasn't created; navigation parameter binding resolves to null.

Related errors

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/e421ab1c4a4637fd. Report an issue: GitHub.