vue watcher errors

Error in callback for watcher TypeError: Cannot set property of undefined”

    newHeaderFilterData (val, oldVal) {
        // update
        // console.log('filter val =', JSON.stringify(val, null, 4));
        // console.log('filter this.packageList =', JSON.stringify(this.packageList, null, 4));
        // if(val.app_id !== oldVal.app_id) {
        //     this.packagesOptions= [];
        //     if(val.app_id.length) {
        //         const apps = val.app_id.split(',');
        //         this.packagesOptions = this.packageList.filter(({value, packageId}) => apps.includes(value));
        //     } else {
        //         this.packagesOptions = this.packageList || [];
        //     }
        //     console.log('new  this.packagesOptions =', JSON.stringify(this.packagesOptions, null, 4));
        // } else {
        //     this.packagesOptions = this.packageList || [];
        // }
    },
    packageList: {
        handler: (val, oldVal) => {
            console.log('filter val =', JSON.stringify(val, null, 4));
            this.packagesOptions = val;
        },
        deep: true,
        // immediate: true,
    },

    <el-form-item
        class="bind-master-modal-form-item"
        v-for="({
            label,
            key,
        }, index) in items"
        :key="index"
        :label="label"
        :label-width="formLabelWidth">
        <TokenSelect
            :selectModel="form[key]"
            :selectOptions="packagesOptions"
            :selectKey="key"
            @search-event="searchHandler"
            @select-event="selectHandler"
        />
    </el-form-item>

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