云数据库的fieldrules怎样判断空数组

目的要实现images或content至少有一个不为空，以下是schema文件

//云数据库schema文件  
"fieldRules": [{  
    "rule": " images.length > 0 || content != '' ",  
         "errorMessage": "content error"  
    }],  
..........  
        "images": {  
            "bsonType": "array",  
            "title": "图片",  
            "description": "图片",  
            "label": "图片",  
            "arrayType": "file",  
            "multiple": true,  
            "fileMediaType": "image",  
            "fileExtName": "jpg,png,jpeg",   
            "maxLength": 9   
        },  
        "content": {  
            "bsonType": "string",  
            "title": "文字部分",  
            "description": "文字部分",  
            "label": "文字内容"  
        },

在schema2code生成的add页面下：

<uni-forms-item name="images" label="图片">
<uni-file-picker file-mediatype="image" file-extname="jpg,png,jpeg" :limit="9" return-type="array" v-model="formData.images"></uni-file-picker>
</uni-forms-item>
<uni-forms-item name="content" label="文字部分">
<uni-easyinput placeholder="文字部分" v-model="formData.content"></uni-easyinput>
</uni-forms-item>

提交uni-form表单时，只有content的非空验证生效，images即使上传了图片也验证失败

请问对于数组类型的非空检测，fieldrules的写法是怎样的？