[known issue] omitempty or not?

[jmnote]

Should we use omitempty for optionals or not?

1. optional in the nbformat spec and omitempty

• metadata.kernelspec.language
• cell.execution_count

If the original JSON contains these keys with empty strings ("") or null values, the keys and values will be omitted in the result due to omitempty.

• https://github.com/jupyter/nbconvert/blob/v7.16.4/tests/files/latex-linked-image.ipynb?short_path=8588232#L14
• https://github.com/jupyter/nbconvert/blob/v7.16.4/tests/files/Unexecuted_widget.ipynb?short_path=c8672d3#L5

2. optional in the nbformat spec, but NOT omitempty

• cell.outputs

outputs in cells are optional, but sometimes we also want the outputs to be empty slices ("outputs": []). So, it should not be omitted.

Therefore, even if the original JSON cells do not have an outputs key or if the value of outputs is null, the cells in the result will always include "outputs": [].

• https://github.com/jupyter/nbconvert/blob/v7.16.4/tests/files/markdown_display_priority.ipynb?short_path=f5669fb#L51

---

Possible solution: We need omitnil.
See golang/go#22480

[jmnote]

required varies depending on the nbformat version and cell type.

• https://github.com/jupyter/nbformat/blob/v5.10.4/nbformat/v4/nbformat.v4.0.schema.json
• https://github.com/jupyter/nbformat/blob/v5.10.4/nbformat/v4/nbformat.v4.4.schema.json
• https://github.com/jupyter/nbformat/blob/v5.10.4/nbformat/v4/nbformat.v4.5.schema.json

// v4.0 - v4.4
// raw_cell:      "required": [      "cell_type", "metadata", "source"]
// markdown_cell: "required": [      "cell_type", "metadata", "source"]
// code_cell:     "required": [      "cell_type", "metadata", "source", "outputs", "execution_count"]

// v4.5
// raw_cell:      "required": ["id", "cell_type", "metadata", "source"]
// markdown_cell: "required": ["id", "cell_type", "metadata", "source"]
// markdown_cell: "required": ["id", "cell_type", "metadata", "source", "outputs", "execution_count"]

From v4.0 to v4.5, metadata.kernelspec.language is optional.