Ignore headers with null values in web cmdlets (#11424)

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/Common/WebRequestPSCmdlet.Common.cs

@@ -663,8 +663,15 @@ namespace Microsoft.PowerShell.Commands
             {
                 foreach (string key in Headers.Keys)
                 {
-                    // add the header value (or overwrite it if already present)
-                    WebSession.Headers[key] = Headers[key].ToString();
+                    var value = Headers[key];
+
+                    // null is not valid value for header.
+                    // We silently ignore header if value is null.
+                    if (!(value is null))
+                    {
+                        // add the header value (or overwrite it if already present)
+                        WebSession.Headers[key] = value.ToString();
+                    }
                 }
             }
 

test/powershell/Modules/Microsoft.PowerShell.Utility/WebCmdlets.Tests.ps1

@@ -3496,4 +3496,19 @@ Describe "Web cmdlets tests using the cmdlet's aliases" -Tags "CI", "RequireAdmi
         $result = Invoke-RestMethod $uri
         $result.Hello | Should -Be "world"
     }
+
+    It "Web cmdlets ignore headers with null value" {
+        $query = @{
+            body        = "hello"
+            contenttype = 'text/plain'
+        }
+        $uri = Get-WebListenerUrl -Test 'Response' -Query $query
+
+        # Core throws if a header has null value.
+        # We ignore such headers so no exception is expected.
+        { Invoke-WebRequest -Uri $uri -Headers @{ "Location" = $null } } | Should -Not -Throw
+        { Invoke-WebRequest -Uri $uri -ContentType $null } | Should -Not -Throw
+        { Invoke-RestMethod -Uri $uri -Headers @{ "Location" = $null } } | Should -Not -Throw
+        { Invoke-RestMethod -Uri $uri -ContentType $null } | Should -Not -Throw
+    }
 }