From 5f92117b97d4e32a39da0b0e8bff3bb6c7317837 Mon Sep 17 00:00:00 2001
From: Dongbo Wang <dongbow@microsoft.com>
Date: Fri, 4 Mar 2022 11:25:01 -0800
Subject: [PATCH] Allow a collection with 'Automation.Null' elements to be
 piped to pipeline

---
 .../engine/Pipe.cs                            | 23 +++++++++++++++----
 .../Scripting/PipelineBehaviour.Tests.ps1     | 21 +++++++++++++++++
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/src/System.Management.Automation/engine/Pipe.cs b/src/System.Management.Automation/engine/Pipe.cs
index 9e24c6471db..2669e41ce31 100644
--- a/src/System.Management.Automation/engine/Pipe.cs
+++ b/src/System.Management.Automation/engine/Pipe.cs
@@ -559,15 +559,28 @@ internal object Retrieve()
             else if (_enumeratorToProcess != null)
             {
                 if (_enumeratorToProcessIsEmpty)
-                    return AutomationNull.Value;
-
-                if (!ParserOps.MoveNext(_context, null, _enumeratorToProcess))
                 {
-                    _enumeratorToProcessIsEmpty = true;
                     return AutomationNull.Value;
                 }
 
-                return ParserOps.Current(null, _enumeratorToProcess);
+                while (true)
+                {
+                    if (!ParserOps.MoveNext(_context, errorPosition: null, _enumeratorToProcess))
+                    {
+                        _enumeratorToProcessIsEmpty = true;
+                        return AutomationNull.Value;
+                    }
+
+                    object retValue = ParserOps.Current(errorPosition: null, _enumeratorToProcess);
+                    if (retValue == AutomationNull.Value)
+                    {
+                        // 'AutomationNull.Value' from the enumerator won't be sent to the pipeline.
+                        // We try to get the next value in this case.
+                        continue;
+                    }
+
+                    return retValue;
+                }
             }
             else if (ExternalReader != null)
             {
diff --git a/test/powershell/Language/Scripting/PipelineBehaviour.Tests.ps1 b/test/powershell/Language/Scripting/PipelineBehaviour.Tests.ps1
index 0478492c910..04993c80a9f 100644
--- a/test/powershell/Language/Scripting/PipelineBehaviour.Tests.ps1
+++ b/test/powershell/Language/Scripting/PipelineBehaviour.Tests.ps1
@@ -602,3 +602,24 @@ Describe 'Function Pipeline Behaviour' -Tag 'CI' {
         #>
     }
 }
+
+Describe 'Other Pipeline Behaviour' -Tag 'CI' {
+    It "Array with 'Automation.Null' elements can be piped to pipeline" {
+        $automationNull = & {}
+
+        ## 'Automation.Null' elements will not be sent to the pipeline (skipped).
+        1, $automationNull, 2, $automationNull, 3, 4, 5 | ForEach-Object { $_ } | Should -Be (1..5)
+        $array = 1, $automationNull, 2, $automationNull, 3, 4, 5
+        $array.Count | Should -Be 7
+        $array | ForEach-Object { $_ } | Should -Be (1..5)
+    }
+
+    It "Automation.Null is not written to pipeline in a function" {
+        $automationNull = & {}
+
+        function MyTest { 1, $automationNull, 2, $automationNull, 3, 4, 5 }
+        $result = MyTest
+        $result.Count | Should -Be 5
+        MyTest | Should -Be (1..5)
+    }
+}