static schema () {
    return {
      username: String,
      childs: [{
       type: Schema.ObjectId,
        ref: 'UserSchema'
      email: {
        type: String,
        type: String,
        required: true,
        unique: true,
        lowercase: true,
        trim: true,
        validate: {
          validator: function (val) {
            return isEmail(val)
          message: '{VALUE} is not a valid email'
apparently the scope of the schema variable, has been lost