MSFT_xExchImapSettings,MSFT_xExchPopSettings ExternalConnectionSettings can be $null

[jrdbarnes]

Details of the scenario you tried and the problem that is occurring

It is a valid configuration option to set ExternalConnectionSettings =$null in Set-PopSettings or Set-IMAPSettings.

The above DSC resources have ExternalConnectionSettings with explicit typing as Strings. I was able to pass empty strings, but maybe they should also be decorated with [AllowEmptyString()]

The Empty Strings are passed directly to Set-PopSettings or Set-IMAPSettings which rejects them as empty strings, but would allow $null. There is already a helper available to do this conversion which is is used in the test

Verbose logs showing the problem

Suggested solution to the issue

Adding
Set-EmptyStringParamsToNull -PSBoundParametersIn $PSBoundParameters

to
https://github.com/dsccommunity/xExchange/blob/3277f2aa8a4a7472fc8610507deecfec54413b29/source/DSCResources/MSFT_xExchPopSettings/MSFT_xExchPopSettings.psm1#L105
https://github.com/dsccommunity/xExchange/blob/3277f2aa8a4a7472fc8610507deecfec54413b29/source/DSCResources/MSFT_xExchImapSettings/MSFT_xExchImapSettings.psm1#L681

The DSC configuration that is used to reproduce the issue (as detailed as possible)

$invokeParams = @{
    name = 'xExchImapSettings',
    module  = @{
      modulename    = 'xExchange',
      moduleversion = '1.27.0.0'
    },
    Method     = 'set'
    properties    = @{
      'server'                     = 'servername',
      'allowServiceRestart'   = $false,
      'loginType'                  = 'PlaintextLogin',
      'externalConnectionSettings' = @(""),
      'credential'                 = $exchangecredential,
    }
  }
Invoke-DscResource @InvokeParams

$invokeParams = @{
    name = 'xExchPopSettings',
    module        = @{
      modulename    = 'xExchange',
      moduleversion = '1.27.0.0'
    },
    properties    => {
      'server'                     = 'servername',
      'allowServiceRestart'        = $false,
      'loginType'                  = 'PlaintextLogin',
      'externalConnectionSettings' = @(""),
      'credential'                 = $exchangecredential,
    }
  }
Invoke-DscResource @InvokeParams

Exchange Server edition and version the target node is running

Exchange Server 2019 CU 4

The operating system the target node is running

OsName : Microsoft Windows Server 2019 Standard
OsOperatingSystemSKU : StandardServerEdition
OsArchitecture : 64-bit
WindowsVersion : 1809
WindowsBuildLabEx : 17763.1.amd64fre.rs5_release.180914-1434
OsLanguage : en-US
OsMuiLanguages : {en-US}

Version and build of PowerShell the target node is running

Name Value
PSVersion 5.1.17763.1432
PSEdition Desktop
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
BuildVersion 10.0.17763.1432
CLRVersion 4.0.30319.42000
WSManStackVersion 3.0
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1

Version of the DSC module that was used

Name Version Path
xExchange 1.27.0.0 C:\Program Files\WindowsPowerShell\Modules\xExchange\1.27.0.0\xExchange.psd1