build-indexes: JSON stringify ignores undefined values used for overriding

[andrebastosdias]

I don't know if this is a known issue. In build-tools/build-indexes, the line

buf += `exports.BattleTeambuilderTable = JSON.parse('${JSON.stringify(BattleTeambuilderTable).replace(/['\\]/g, "\\$&")}');\n\n`;

ignores undefined values. I was trying to override the requiredItem for Giratina-Origin, Palkia-Origin and Dialga-Origin for a mod, but it kept putting the item in the teambuilder when I selected them.
I changed the line to

buf += `exports.BattleTeambuilderTable = JSON.parse('${JSON.stringify(BattleTeambuilderTable, (k, v) => (v === undefined) ? null : v).replace(/['\\]/g, "\\$&")}');\n\n`;

but I don't know if it may cause any undesirable behaviour.