如何在猫鼬模式中设置数组对象的默认值？

Question

我为此尝试了许多方法。我还找不到正确的方法。请查看收藏夹array对象和默认值。当我保存它时，数组对象的一部分不包含null对象。

const mongoose = require('mongoose');
const MemberSettingSchema = new mongoose.Schema({
    organization: {
        type: String,
        unique: true,
        required: true,
    },
    favorites: {
        type: Array,
        validate: {
            validator: function() {
                return this.favorites.length <= 20;
            },
            message: 'Array exceeds max size.'
        },
        name: {
            type: String,
            default: null,
            required: true,
        },
        //Custom part
        customImplantOrganization: {
            type: String,
            required: true,
            enum: ['A', 'B', 'C'],
            default: null,
        },
        customImplantType: {
            type: String,
            enum: ['D', 'F'],
            default: null,
        },
        customImplantSize: {
            type: String,
            enum: ['E', 'Q'],
            default: null,
        },
        customHexOption: {
            type: String,
            enum: ['P'],
            default: null,
        },
        customProcessManner: {
            type: String,
            enum: ['7', '6'],
            default: null,
        },
        customOption: {
            type: String,
            enum: ['2', '3', '4'],
            default: null,
        },
        //Crown part
        crownShade: {
            type: String,
            enum: ['91'],
            default: [null],
        },
        crownStrength: {
            type: String,
            enum: ['7', '78'],
            default: null,
        },
        crownOption: {
            type: String,
            enum: ['9'],
            default: undefined,
        },
        wasCreated: {
            type: Boolean,
            default: false,
        },
    },
    modifiedBy: {
        type: String,
        default: null,
    },
    modifiedTime: {
        type: Date,
        default: null
    },
});
module.exports = mongoose.model('memberSetting', MemberSettingSchema);