节点json-schema阻止整数的null

I have schema,

我有架构,

'demand': {
    description: 'demand model',
    type: 'object',
    additionalProperties: false,
    properties: {
        '_id': {
            type: 'string'
        },
        'driversNeeded': {
            required: true,
            type: 'integer',
            minumum: 0
        },
        'date': {
            required: true,
            type: 'string',
            pattern: /^\d{4}-\d{2}-\d{2}$/
        }
    }
}
'demand': {
    descri