Output format: Which properties (if any) can be null or omitted?

For a valid Editor.js document, can any of the top-level `time`, `blocks`, and `version` properties, or the block-level `type` and `data` properties, under any circumstances (now or in the future) be `null` or omitted? Or are they guaranteed to always be present and non-`null` for a document to be valid? Does whether `data` is null/present for a block depend on the block type?

Context: I'm a back-end .NET developer needing to parse Editor.js documents. [The docs on the output format](https://editorjs.io/saving-data#output-data-format) lists all of the aforementioned properties but does not explicitly guarantee that they will always be present and non-null. Back-end deserialization/parsing in strongly typed languages would be easier with some guarantees about which properties can and can not be null/omitted. (Ideally, any such guarantees should be added to the documentation to ensure they are formalized and kept in the future.)