From dc38b451bee4bdf07f7200026be02516807faa09 Mon Sep 17 00:00:00 2001
From: Dongbo Wang <dongbow@microsoft.com>
Date: Thu, 11 Mar 2021 09:14:44 -0800
Subject: [PATCH] Fix a null-ref exception in `DynamicHelpImpl` (#2292)

---
 PSReadLine/DynamicHelp.cs |  3 +++
 test/DynamicHelpTest.cs   | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/PSReadLine/DynamicHelp.cs b/PSReadLine/DynamicHelp.cs
index b59bd15a..bffa4ac9 100644
--- a/PSReadLine/DynamicHelp.cs
+++ b/PSReadLine/DynamicHelp.cs
@@ -151,6 +151,9 @@ private void DynamicHelpImpl(bool isFullHelp)
             string commandName = null;
             string parameterName = null;
 
+            // Simply return if nothing is rendered yet.
+            if (_singleton._tokens == null) { return; }
+
             foreach(var token in _singleton._tokens)
             {
                 var extent = token.Extent;
diff --git a/test/DynamicHelpTest.cs b/test/DynamicHelpTest.cs
index 5470f930..68c1d184 100644
--- a/test/DynamicHelpTest.cs
+++ b/test/DynamicHelpTest.cs
@@ -97,6 +97,13 @@ private static PSObject GetParameterHelpObject(string description)
             return paramHelp;
         }
 
+        [SkippableFact]
+        public void DynHelp_GetFullHelp_OnEmptyLine()
+        {
+            TestSetup(KeyMode.Cmd);
+            Test("", Keys(_.F1, _.Enter));
+        }
+
         [SkippableFact]
         public void DynHelp_GetFullHelp()
         {
@@ -108,6 +115,13 @@ public void DynHelp_GetFullHelp()
                 ));
         }
 
+        [SkippableFact]
+        public void DynHelp_GetParameterHelp_OnEmptyLine()
+        {
+            TestSetup(KeyMode.Cmd);
+            Test("", Keys(_.Alt_h, _.Enter));
+        }
+
         [SkippableFact]
         public void DynHelp_GetParameterHelp_And_Clear()
         {