getByHandle(handle) {
        if (!handle.isValid) {
            return null;
        }
        const ent = this.entities.get(handle.index);
        if (ent == null || ent.serialNum !== handle.serialNum) {
            return null;
        }
        return ent;
    }
Returns the entity specified by a particular handle.
@param {number} handle - Networked entity handle value
@returns {Entity|null} Entity referenced by the handle. `null` if no matching entity.