PSUseOutputTypeCorrectly/[OutputType()] fires incorrectly, reporting that a fn should return string when the function actually return array of strings

Before submitting a bug report:

• Make sure you are able to repro it on the latest released version
• Perform a quick search for existing issues to check if this bug has already been reported

Steps to reproduce

function Split-KeyValuePairFormatter {
  [OutputType('System.String[]')]
  [CmdletBinding()]
  param (
    [Parameter(Mandatory = $true)]
    [string]
    $Format,

    [string]
    $KeyConstituent,

    [string]
    $ValueConstituent,

    [string]
    $KeyPlaceHolder = "<%KEY%>",

    [string]
    $ValuePlaceHolder = "<%VALUE%>"
  )
  [string[]]$constituents = @();

   # IMPLEMENTATION CODE OMITTED, but you can see that the return statement
   # just returns the array declared as string[]

   return $constituents;
}

Expected behavior

No warning expected

Actual behavior

Error:

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
PSUseOutputTypeCorrectly            Information  split-key- 152   The cmdlet 'Split-KeyValuePairFormatter' returns an  
                                                 value-pair       object of type 'System.String' but this type is not  
                                                 -formatter       declared in the OutputType attribute.
                                                 .ps1

If I change OutputType to: [OutputType('System.String')], which is clearly wrong as it doesn't reflect the behaviour of the actual code, then there is no error. This does not seem right. As a work around, I'm having to declare an incorrect return type, ie System.string in [OutputType()], and put in a comment to indicate as such. Luckily, there is no effect on the functinality, but I can't omit the OutputType without PSScriptAnalyzer reporting a warning.

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.0.0
PSEdition                      Core
GitCommitId                    7.0.0
OS                             Microsoft Windows 10.0.18362
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }
1.19.0
1.18.3

Comienza reproduciendo la advertencia PSUseOutputTypeCorrectly con el ejemplo Split-KeyValuePairFormatter e inspecciona cómo la regla gestiona OutputType('System.String[]'). Compara el tipo de retorno inferido con el tipo de array declarado. Se considera terminado cuando la regla acepta el retorno de un array de strings sin requerir una declaración incorrecta de System.String.