diff --git a/src/Workspaces/CSharp/Portable/Indentation/CSharpIndentationService.Indenter.cs b/src/Workspaces/CSharp/Portable/Indentation/CSharpIndentationService.Indenter.cs
index bcd53246f399e20c4b3c92d90979e6e3256a067d..3a939e4f22e67e60c39452da9277112273deca10 100644
--- a/src/Workspaces/CSharp/Portable/Indentation/CSharpIndentationService.Indenter.cs
+++ b/src/Workspaces/CSharp/Portable/Indentation/CSharpIndentationService.Indenter.cs
@@ -31,9 +31,9 @@ protected override ISmartTokenFormatter CreateSmartTokenFormatter(Indenter inden
             return new CSharpSmartTokenFormatter(indenter.OptionSet, rules, indenter.Root);
         }
 
-        protected override IndentationResult GetDesiredIndentationWorker(Indenter indenter, SyntaxToken? tokenOpt, SyntaxTrivia? triviaOpt)
+        protected override IndentationResult? GetDesiredIndentationWorker(Indenter indenter, SyntaxToken? tokenOpt, SyntaxTrivia? triviaOpt)
             => TryGetDesiredIndentation(indenter, triviaOpt) ??
-               TryGetDesiredIndentation(indenter, tokenOpt) ?? default;
+               TryGetDesiredIndentation(indenter, tokenOpt);
 
         private IndentationResult? TryGetDesiredIndentation(Indenter indenter, SyntaxTrivia? triviaOpt)
         {
diff --git a/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.Indenter.cs b/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.Indenter.cs
index c349f3225fe9b15bb02cce96a3340525cbefea0e..275167de12a41aceb1754863816a6fa7e07fd22b 100644
--- a/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.Indenter.cs
+++ b/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.Indenter.cs
@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -50,7 +52,7 @@ protected struct Indenter
                 Document = document;
 
                 _service = service;
-                _syntaxFacts = document.Document.GetLanguageService<ISyntaxFactsService>();
+                _syntaxFacts = document.Document.GetRequiredLanguageService<ISyntaxFactsService>();
                 OptionSet = optionSet;
                 OptionService = document.Document.Project.Solution.Workspace.Services.GetRequiredService<IOptionService>();
                 Root = (TSyntaxRoot)document.Root;
@@ -66,11 +68,11 @@ protected struct Indenter
                     tokenStream: null);
             }
 
-            public IndentationResult GetDesiredIndentation(FormattingOptions.IndentStyle indentStyle)
+            public IndentationResult? GetDesiredIndentation(FormattingOptions.IndentStyle indentStyle)
             {
                 // If the caller wants no indent, then we'll return an effective '0' indent.
                 if (indentStyle == FormattingOptions.IndentStyle.None)
-                    return default;
+                    return null;
 
                 // If the user has explicitly set 'block' indentation, or they're in an inactive preprocessor region,
                 // then just do simple block indentation.
@@ -84,7 +86,7 @@ public IndentationResult GetDesiredIndentation(FormattingOptions.IndentStyle ind
                 return GetDesiredSmartIndentation();
             }
 
-            private readonly IndentationResult GetDesiredSmartIndentation()
+            private readonly IndentationResult? GetDesiredSmartIndentation()
             {
                 // For smart indent, we generally will be computing from either the previous token in the code, or in a
                 // few special cases, the previous trivia.
@@ -97,7 +99,7 @@ public IndentationResult GetDesiredIndentation(FormattingOptions.IndentStyle ind
                 var trivia = TryGetImmediatelyPrecedingVisibleTrivia();
 
                 if (token == null && trivia == null)
-                    return default;
+                    return null;
 
                 return _service.GetDesiredIndentationWorker(this, token, trivia);
             }
@@ -143,7 +145,7 @@ public IndentationResult GetDesiredIndentation(FormattingOptions.IndentStyle ind
                 return token;
             }
 
-            private IndentationResult GetDesiredBlockIndentation()
+            private IndentationResult? GetDesiredBlockIndentation()
             {
                 // Block indentation is simple, we keep walking back lines until we find a line with any sort of
                 // text on it.  We then set our indentation to whatever the indentation of that line was.
@@ -158,8 +160,8 @@ private IndentationResult GetDesiredBlockIndentation()
                     return new IndentationResult(basePosition: line.Start + offset.Value, offset: 0);
                 }
 
-                // Couldn't find a previous non-blank line.  Don't indent at all.
-                return default;
+                // Couldn't find a previous non-blank line.
+                return null;
             }
 
             public bool TryGetSmartTokenIndentation(out IndentationResult indentationResult)
diff --git a/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.cs b/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.cs
index 1596ad1e09504d95df833e0934d0cd15164907eb..d0ca40d8e9b9faf0194e30b9aff0e2030c33cb56 100644
--- a/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.cs
+++ b/src/Workspaces/Core/Portable/Indentation/AbstractIndentationService.cs
@@ -2,12 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.Formatting;
 using Microsoft.CodeAnalysis.Formatting.Rules;
-using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Indentation
@@ -45,7 +46,8 @@ private IEnumerable<AbstractFormattingRule> GetFormattingRules(Document document
                 return indentationResult;
             }
 
-            return indenter.GetDesiredIndentation(indentStyle);
+            // If the indenter can't produce a valid result, just default to 0 as our indentation.
+            return indenter.GetDesiredIndentation(indentStyle) ?? default;
         }
 
         private Indenter GetIndenter(Document document, int lineNumber, FormattingOptions.IndentStyle indentStyle, CancellationToken cancellationToken)
@@ -70,7 +72,7 @@ private Indenter GetIndenter(Document document, int lineNumber, FormattingOption
         protected abstract bool ShouldUseTokenIndenter(Indenter indenter, out SyntaxToken token);
         protected abstract ISmartTokenFormatter CreateSmartTokenFormatter(Indenter indenter);
 
-        protected abstract IndentationResult GetDesiredIndentationWorker(
+        protected abstract IndentationResult? GetDesiredIndentationWorker(
             Indenter indenter, SyntaxToken? token, SyntaxTrivia? trivia);
     }
 }
diff --git a/src/Workspaces/VisualBasic/Portable/Indentation/VisualBasicIndentationService.Indenter.vb b/src/Workspaces/VisualBasic/Portable/Indentation/VisualBasicIndentationService.Indenter.vb
index 56bac90b17e1d3aed8729f617ae84bcd239e7221..b774dc108bb4e23ed5d45401b0b73a21d34d4f9e 100644
--- a/src/Workspaces/VisualBasic/Portable/Indentation/VisualBasicIndentationService.Indenter.vb
+++ b/src/Workspaces/VisualBasic/Portable/Indentation/VisualBasicIndentationService.Indenter.vb
@@ -27,7 +27,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Indentation
         Protected Overrides Function GetDesiredIndentationWorker(
                 indenter As Indenter,
                 tokenOpt As SyntaxToken?,
-                triviaOpt As SyntaxTrivia?) As IndentationResult
+                triviaOpt As SyntaxTrivia?) As IndentationResult?
 
             If triviaOpt.HasValue Then
                 Dim trivia = triviaOpt.Value