Only add files to module if module is not null.

src/Generator/Driver.cs

@@ -319,6 +319,8 @@ namespace CppSharp
 
                     var file = Path.Combine(outputPath, fileRelativePath);
                     WriteGeneratedCodeToFile(file, template.Generate());
+
+                    if (output.TranslationUnit.Module != null)
                         output.TranslationUnit.Module.CodeFiles.Add(file);
 
                     Diagnostics.Message("Generated '{0}'", fileRelativePath);