What causes "Document has no MainDocumentPart." in MiniMax-AI/skills?

MiniMax-AI/skills · critical · InvalidOperationException

Document has no MainDocumentPart.

Error message

Document has no MainDocumentPart.

What it means

`doc.MainDocumentPart ?? throw new InvalidOperationException("Document has no MainDocumentPart.")` in the reference `AddFullComment` helper. OpenXML's `WordprocessingDocument.MainDocumentPart` is the part that holds `word/document.xml` (the body text). It is null when the package was created without a main part or opened from a malformed/empty package. The reference code refuses to operate because every comment operation reads and writes the document body through this part.

Source

Thrown at skills/minimax-docx/references/openxml_encyclopedia_part3.md:1364

## 5. Comments (4-File System)

### 5.1 Full 4-File Comment System Setup

Comments require four XML files plus markers in `document.xml`.

```csharp
// This method creates a complete comment with all 4 files properly initialized
public static int AddFullComment(
    WordprocessingDocument doc,
    string text,
    string author,
    string initials,
    string rangeText,
    int? existingCommentId = null)
{
    var mainPart = doc.MainDocumentPart
        ?? throw new InvalidOperationException("Document has no MainDocumentPart.");

    int commentId = existingCommentId ?? GetNextCommentId(doc);

    // Generate paraId (8-char hex) and durableId (8-digit hex)
    string paraId = Guid.NewGuid().ToString("N")[..8].ToUpperInvariant();
    string durableId = new Random().Next(0x10000000, 0xFFFFFFFF).ToString("X8");

    var body = mainPart.Document!.Body!;

    // ─────────────────────────────────────────────────────────────
    // FILE 1: word/comments.xml — Main comment content
    // ─────────────────────────────────────────────────────────────
    var commentsPart = mainPart.WordprocessingCommentsPart
        ?? mainPart.AddNewPart<WordprocessingCommentsPart>();

    if (commentsPart.Comments == null)
        commentsPart.Comments = new Comments();

View on GitHub (pinned to 60aaae52bb)

Solutions

When creating new documents, initialize the part: `var main = doc.AddMainDocumentPart(); main.Document = new Document(new Body());` before calling comment methods.
When opening existing files, verify the source is a valid Word document (not a `.dotx` template or empty file) with `doc.MainDocumentPart != null` before use.
Use `WordprocessingDocument.Open(path, true)` on a real `.docx`; if it lacks a main part, recreate it from a known-good template.

Example fix

// before — throws on a fresh doc
using var doc = WordprocessingDocument.Create(path, WordprocessingDocumentType.Document);
AddFullComment(doc, "hi", "me", "MJ");

// after — seed the main part first
using var doc = WordprocessingDocument.Create(path, WordprocessingDocumentType.Document);
var main = doc.AddMainDocumentPart();
main.Document = new Document(new Body());
AddFullComment(doc, "hi", "me", "MJ");

Defensive patterns

Strategy: validation

Validate before calling

void EnsureMainPart(WordprocessingDocument doc)
{
    if (doc.MainDocumentPart is null)
    {
        var main = doc.AddMainDocumentPart();
        main.Document = new Document(new Body());
    }
}

// before any comment operation
EnsureMainPart(doc);

Type guard

bool HasMainPart(WordprocessingDocument doc) => doc.MainDocumentPart is not null;

Try / catch

try
{
    AddFullComment(doc, text, author, initials, rangeText);
}
catch (InvalidOperationException ex) when (ex.Message.Contains("MainDocumentPart"))
{
    // seed the part and retry once
    var main = doc.AddMainDocumentPart();
    main.Document = new Document(new Body());
    AddFullComment(doc, text, author, initials, rangeText);
}

Prevention

Always call `AddMainDocumentPart()` and seed a `Document(new Body())` immediately after `WordprocessingDocument.Create`.
Open from a known-good `.docx` template instead of creating empty packages when you need a full document.
Centralize document creation in one factory method that guarantees a non-null main part.
Assert `doc.MainDocumentPart != null` in debug builds before any manipulation.

When it happens

Trigger: Calling `AddFullComment` on a `WordprocessingDocument` created with `WordprocessingDocument.Create(path, WordprocessingDocumentType.Document)` but no `AddMainDocumentPart()` was ever called, or on a `.docx` that is actually a template/empty shell missing `word/document.xml`.

Common situations: Creating a brand-new document and forgetting to initialize the main part, opening a `.docx` that is really a macro-enabled template or a corrupt package, or chaining operations on a document that was closed/disposed.

Related errors

AI-assisted analysis of MiniMax-AI/skills@60aaae52bb (2026-08-13). Data as JSON: /api/errors/f4da7436808a71a6. Report an issue: GitHub.