Bicep中的可选参数可以使用?符号来标记。下面是一个示例，其中name和url参数都是可选的：

param storageAccountName string
param containerName string
param name string = ''
param url string = ''

resource storageAccount 'Microsoft.Storage/storageAccounts@2019-06-01' = {
  name: storageAccountName
  ...
}

resource container 'Microsoft.Storage/storageAccounts/blobServices/containers@2021-08-01-preview' = {
  parent: storageAccount
  name: containerName
  ...
}

resource file 'Microsoft.Storage/storageAccounts/blobServices/containers/blobs@2021-08-01-preview' = {
  parent: container
  name: '${name}.txt'
  url: url
  ...
}