Allow Set-Clipboard to accept empty string (#14579)

test/powershell/Modules/Microsoft.PowerShell.Management/Clipboard.Tests.ps1

@@ -41,5 +41,15 @@ Describe 'Clipboard cmdlet tests' -Tag CI {
             'world' | Set-Clipboard -Append
             Get-Clipboard -Raw | Should -BeExactly "hello$([Environment]::NewLine)world"
         }
+
+        It 'Set-Clipboard accepts <value> string' -TestCases @(
+            @{ value = 'empty'; text = "" }
+            @{ value = 'null' ; text = $null }
+        ){
+            param ($text)
+
+            $text | Set-Clipboard
+            Get-Clipboard -Raw | Should -BeNullOrEmpty
+        }
     }
 }