dotnet/wpf · error · ArgumentNullException

ArgumentNullException: destinationFileBaseName

Error message

ArgumentNullException: destinationFileBaseName

What it means

TaskFileService.WriteGeneratedCodeFile writes generated code to a build file and an intellisense file derived from destinationFileBaseName. It throws ArgumentNullException when destinationFileBaseName is null or empty because the output file paths cannot be constructed.

Solutions

  1. Ensure the base name (typically IntermediateOutputPath + file name) is non-empty before calling.
  2. Check that $(IntermediateOutputPath) and related properties are set in the build environment.
  3. Add an early validation in the calling task that reports which property was empty.

Example fix

// before
fileService.WriteGeneratedCodeFile(content, baseName, ".g.cs", ".g.i.cs", "");
// after
if (string.IsNullOrEmpty(baseName))
    throw new ArgumentException("Generated file base name is required", nameof(baseName));
fileService.WriteGeneratedCodeFile(content, baseName, ".g.cs", ".g.i.cs", "");
Defensive patterns

Strategy: validation

Validate before calling

if (string.IsNullOrEmpty(destinationFileBaseName))
    throw new ArgumentException("destinationFileBaseName must be non-empty", nameof(destinationFileBaseName));

Type guard

bool HasBaseName(string s) => !string.IsNullOrEmpty(s);

Try / catch

try { fileService.WriteGeneratedCodeFile(content, baseName, ext, iext, langExt); }
catch (ArgumentNullException ex) { log.Error($"Missing generated-file base name: {ex.ParamName}"); throw; }

Prevention

When it happens

Trigger: Calling WriteGeneratedCodeFile(byte[] contentArray, string destinationFileBaseName, string generatedExtension, string intellisenseGeneratedExtension, string languageSourceExtension) with destinationFileBaseName null or empty.

Common situations: MSBuild intermediate output path or generated file base name resolved to empty during XAML markup compilation, often due to a misconfigured project or an intellisense (design-time) build passing an unset path.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/fddf234acb986e7a. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/MS/Internal/Tasks/TaskFileService.cs:331

        }

        // Save content stream for the given generated code file.
        // This function decides which extension to use for the file
        // and whether to put it into memory or merely write it to
        // disk based on whether it is a real build or an intellisense
        // build operation. It also takes care of deleting the corresponding
        // unused generated file (i.e. if real build then it deletes
        // the intellisense file otherwise it deletes the non-intellisense
        // file.
        // NOTE: UTF8 BOM should not be added to the contentArray.  This
        // method adds BOM before writing file to disk.
        //
        public void WriteGeneratedCodeFile(byte[] contentArray, string destinationFileBaseName,
            string generatedExtension, string intellisenseGeneratedExtension, string languageSourceExtension)
        {
            if (string.IsNullOrEmpty(destinationFileBaseName))
            {
                throw new ArgumentNullException(nameof(destinationFileBaseName));
            }

            if (contentArray == null)
            {
                throw new ArgumentNullException(nameof(contentArray));
            }

            string buildFile = destinationFileBaseName + generatedExtension + languageSourceExtension;
            string intelFile = destinationFileBaseName + intellisenseGeneratedExtension + languageSourceExtension;

            string destinationFile = IsRealBuild ? buildFile : intelFile;

            UTF8Encoding utf8Encoding = new UTF8Encoding();
            string contentStr = utf8Encoding.GetString(contentArray);

            // Add BOM for UTF8Encoding since the input contentArray is not supposed to
            // have it already.
            using (StreamWriter sw = new StreamWriter(destinationFile, false, new UTF8Encoding(true)))

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