fix: toDelta should ignore entries with null value

[zxch3n]

Fix the issue mentioned in loro-dev/loro-prosemirror#58

[chatgpt-codex-connector]

💡 Codex Review

loro/crates/loro-wasm/src/convert.rs

Lines 780 to 784 in b288c95

	if let Some(attributes) = attributes {
	if !attributes.is_empty() {
	let attrs = Object::new();
	for (k, v) in attributes {
	Reflect::set(&attrs, &k.into(), &convert(v)?)?;

Null attributes still serialized for insert deltas

text_delta_to_js_value now skips null-valued attributes only for retain ops, but toDelta/sliceDelta feed it Insert segments from handler.get_delta(); this branch still copies every attribute value, including LoroValue::Null, straight into the JS object. If a delta applies {attributes: {bold: null}} to drop a style, the resulting toDelta output will still include attributes: { bold: null } on the affected inserts, so consumers cannot tell the style was removed. The Insert branch needs the same null filtering as the Retain branch to satisfy the commit goal.

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WASM Size Report

• Original size: 3183.93 KB
• Gzipped size: 1008.57 KB
• Brotli size: 700.21 KB