PrismLibrary/Prism · error · ArgumentException

Resources.StringCannotBeNullOrEmpty (formatted with…

Error message

Resources.StringCannotBeNullOrEmpty (formatted with 'dependingModule')

What it means

ModuleDependencySolver.AddDependency throws ArgumentException with Resources.StringCannotBeNullOrEmpty when dependingModule or dependentModule is null/empty, and DependencyForUnknownModule when dependingModule was never added via AddModule. The solver can only record edges between known module names.

Solutions

Ensure both module names are non-empty and that AddModule was called for the depending module before AddDependency.
Fix DependsOn entries in the module definitions to match exactly the registered ModuleName values.
Use SolveDependencies/ValidateDependencyGraph on the full catalog so all modules are added before dependency edges are resolved.

Example fix

// before
solver.AddDependency("", "Core");
// after
if (!string.IsNullOrEmpty(dependingModule) && !string.IsNullOrEmpty(dependentModule))
{
    solver.AddModule(dependingModule);
    solver.AddDependency(dependingModule, dependentModule);
}

Defensive patterns

Strategy: validation

Validate before calling

var known = modules.Select(m => m.ModuleName).ToHashSet();
foreach (var m in modules)
{
    foreach (var d in m.DependsOn ?? Enumerable.Empty<string>())
    {
        if (string.IsNullOrWhiteSpace(d) || !known.Contains(d))
            throw new InvalidOperationException($"Module '{m.ModuleName}' has invalid dependency '{d}'");
    }
}

Type guard

bool IsKnownDependency(string d, ISet<string> known) => !string.IsNullOrWhiteSpace(d) && known.Contains(d);

Try / catch

try
{
    catalog.Validate();
}
catch (ArgumentException ex)
{
    logger.LogError(ex, "Dependency solver rejected a module/dependency name: {0}", ex.Message);
}

Prevention

Validate DependsOn entries against registered ModuleNames before validation
Strip empty strings from DependsOn arrays when parsing config
Add all modules to the solver before resolving dependency edges

When it happens

Trigger: Calling AddDependency(null, x), AddDependency("", x), AddDependency(x, null), or AddDependency("Unknown", x) where "Unknown" was not previously registered with AddModule; reached indirectly from SolveDependencies when a catalog's DependsOn contains empty strings or references modules added after the dependency pass.

Common situations: DependsOn arrays containing empty entries from config parsing; a typo'd dependency name that matches no registered module; a custom catalog that adds dependencies before adding all modules.

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/6f12ca5c9efa0302. Report an issue: GitHub.

Appendix: source

Thrown at src/Prism.Core/Modularity/ModuleDependencySolver.cs:41

        {
            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))
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, Resources.StringCannotBeNullOrEmpty, "dependentModule"));

            if (!knownModules.Contains(dependingModule))
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, Resources.DependencyForUnknownModule, dependingModule));

            AddToDependencyMatrix(dependentModule);
            dependencyMatrix.Add(dependentModule, dependingModule);
        }

        private void AddToDependencyMatrix(string module)
        {
            if (!dependencyMatrix.ContainsKey(module))
            {
                dependencyMatrix.Add(module);
            }
        }

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