getOrCreateContainer throws an exception when the existing value is null

[optimalstrategy]

One of the documents we're using Loro with has a value that may be null or a container like LoroMap. When the value is null and we try to initialize it with a container using getOrCreateContainer, Loro throws an exception.

It is possible to avoid this error by first checking if the stored value is null and using setContainer in that case. However, I think it would be more ergonomic if getOrCreateContainer treated null values the same way as the field not being initialized at all.

• loro-crdt version: 1.1.4

Example

import { LoroDoc, LoroMap } from "loro-crdt";

const doc = new LoroDoc();
const root = doc.getMap("root");

// No key -- ok
root.getOrCreateContainer("key", new LoroMap());
doc.commit();
console.log(doc.toJSON());

// Set to null  -- ok
root.set("key", null);
doc.commit();
console.log(doc.toJSON());

// Key is null, create a container
try {
    root.getOrCreateContainer("key", new LoroMap());  
} catch (e) {
    console.error(e);  // Invalid argument (Expected value type Map but found Value(Null))
}

// Avoids the error but defeats the purpose of getOrCreateContainer
let inner = root.get("key");
if (!inner) {
    inner = root.setContainer("key", new LoroMap());
}
console.log(doc.toJSON())