Make ConvertTo-Json treat [AutomationNull]::Value and [NullString]::Value as $null (PowerShell#10957)

Author: daxian-dbw

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/JsonObject.cs

@@ -7,6 +7,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Management.Automation;
+using System.Management.Automation.Language;
 using System.Reflection;
 using System.Text.RegularExpressions;
 using System.Threading;
@@ -496,6 +497,11 @@ private static object ProcessValue(object obj, int currentDepth, in ConvertToJso
         {
             context.CancellationToken.ThrowIfCancellationRequested();
 
+            if (LanguagePrimitives.IsNull(obj))
+            {
+                return null;
+            }
+
             PSObject pso = obj as PSObject;
 
             if (pso != null)
@@ -507,18 +513,21 @@ private static object ProcessValue(object obj, int currentDepth, in ConvertToJso
             bool isPurePSObj = false;
             bool isCustomObj = false;
 
-            if (obj == null
-                || DBNull.Value.Equals(obj)
-                || obj is string
-                || obj is char
-                || obj is bool
-                || obj is DateTime
-                || obj is DateTimeOffset
-                || obj is Guid
-                || obj is Uri
-                || obj is double
-                || obj is float
-                || obj is decimal)
+            if (obj == NullString.Value
+                || obj == DBNull.Value)
+            {
+                rv = null;
+            }
+            else if (obj is string
+                    || obj is char
+                    || obj is bool
+                    || obj is DateTime
+                    || obj is DateTimeOffset
+                    || obj is Guid
+                    || obj is Uri
+                    || obj is double
+                    || obj is float
+                    || obj is decimal)
             {
                 rv = obj;
             }

test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertTo-Json.Tests.ps1

@@ -69,4 +69,38 @@ Describe 'ConvertTo-Json' -tags "CI" {
         ConvertTo-Json -Compress $null | Should -Be 'null'
         1, $null, 2 | ConvertTo-Json -Compress | Should -Be '[1,null,2]'
     }
+
+    It "Should handle 'AutomationNull.Value' and 'NullString.Value' correctly" {
+        [ordered]@{
+            a = $null;
+            b = [System.Management.Automation.Internal.AutomationNull]::Value;
+            c = [System.DBNull]::Value;
+            d = [NullString]::Value
+        } | ConvertTo-Json -Compress | Should -BeExactly '{"a":null,"b":null,"c":null,"d":null}'
+
+        ConvertTo-Json ([System.Management.Automation.Internal.AutomationNull]::Value) | Should -BeExactly 'null'
+        ConvertTo-Json ([NullString]::Value) | Should -BeExactly 'null'
+
+        ConvertTo-Json -Compress @(
+            $null,
+            [System.Management.Automation.Internal.AutomationNull]::Value,
+            [System.DBNull]::Value,
+            [NullString]::Value
+        ) | Should -BeExactly '[null,null,null,null]'
+    }
+
+    It "Should handle the ETS properties added to 'DBNull.Value' and 'NullString.Value'" {
+        try
+        {
+            $p1 = Add-Member -InputObject ([System.DBNull]::Value) -MemberType NoteProperty -Name dbnull -Value 'dbnull' -PassThru
+            $p2 = Add-Member -InputObject ([NullString]::Value) -MemberType NoteProperty -Name nullstr -Value 'nullstr' -PassThru
+
+            $p1, $p2 | ConvertTo-Json -Compress | Should -BeExactly '[{"value":null,"dbnull":"dbnull"},{"value":null,"nullstr":"nullstr"}]'
+        }
+        finally
+        {
+            $p1.psobject.Properties.Remove('dbnull')
+            $p2.psobject.Properties.Remove('nullstr')
+        }
+    }
 }