PrismLibrary/Prism · error · ArgumentException

Resources.StringCannotBeNullOrEmpty (formatted with 'name')

Error message

Resources.StringCannotBeNullOrEmpty (formatted with 'name')

What it means

ModuleDependencySolver.AddModule throws ArgumentException with Resources.StringCannotBeNullOrEmpty when the module name is null or empty. Module names are the solver's identity keys for ordering and cycle detection, so a null/empty name is rejected immediately.

Solutions

  1. Set a non-empty ModuleName on every IModuleInfo added to the catalog.
  2. Check the module definition source (code, XAML, app.config) for a missing name attribute.
  3. Add a pre-validation pass that rejects modules with string.IsNullOrWhiteSpace(ModuleName).

Example fix

// before
var module = new ModuleInfo { ModuleType = typeof(MyModule).AssemblyQualifiedName }; // ModuleName empty
// after
var module = new ModuleInfo { ModuleName = "MyModule", ModuleType = typeof(MyModule).AssemblyQualifiedName };
Defensive patterns

Strategy: validation

Validate before calling

if (modules.Any(m => string.IsNullOrWhiteSpace(m.ModuleName)))
    throw new InvalidOperationException("All modules must have a non-empty ModuleName before catalog validation");

Type guard

bool HasName(IModuleInfo m) => !string.IsNullOrWhiteSpace(m?.ModuleName);

Try / catch

try
{
    catalog.Validate();
}
catch (ArgumentException ex) when (ex.Message.Contains("name"))
{
    logger.LogError(ex, "A module with an empty ModuleName reached the dependency solver");
}

Prevention

When it happens

Trigger: Calling solver.AddModule(null) or AddModule("") directly, or indirectly when SolveDependencies iterates a catalog containing an IModuleInfo whose ModuleName is null or empty.

Common situations: Programmatically created ModuleInfo objects with the name forgotten; config/XAML entries missing the module name attribute; data binding that produced an empty name.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/a4ed00110fd9d4d2. Report an issue: GitHub.

Appendix: source

Thrown at src/Prism.Core/Modularity/ModuleDependencySolver.cs:25

namespace Prism.Modularity
{
    /// <summary>
    /// Used by <see cref="IModuleInitializer"/> to get the load sequence
    /// for the modules to load according to their dependencies.
    /// </summary>
    public class ModuleDependencySolver
    {
        private readonly ListDictionary<string, string> dependencyMatrix = new ListDictionary<string, string>();
        private readonly List<string> knownModules = new List<string>();

        /// <summary>
        /// Adds a module to the solver.
        /// </summary>
        /// <param name="name">The name that uniquely identifies the module.</param>
        public void AddModule(string name)
        {
            if (String.IsNullOrEmpty(name))
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, Resources.StringCannotBeNullOrEmpty, "name"));

            AddToDependencyMatrix(name);
            AddToKnownModules(name);
        }

        /// <summary>
        /// Adds a module dependency between the modules specified by dependingModule and
        /// dependentModule.
        /// </summary>
        /// <param name="dependingModule">The name of the module with the dependency.</param>
        /// <param name="dependentModule">The name of the module dependingModule
        /// depends on.</param>
        public void AddDependency(string dependingModule, string dependentModule)
        {
            if (String.IsNullOrEmpty(dependingModule))
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, Resources.StringCannotBeNullOrEmpty, "dependingModule"));

            if (String.IsNullOrEmpty(dependentModule))

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