Feature should not be offered unless user is targetting C# 7 and above.

src/Features/CSharp/Portable/CSharpFeatures.csproj

@@ -354,6 +354,7 @@
     <Compile Include="Organizing\Organizers\OperatorDeclarationOrganizer.cs" />
     <Compile Include="Organizing\Organizers\PropertyDeclarationOrganizer.cs" />
     <Compile Include="Organizing\Organizers\StructDeclarationOrganizer.cs" />
+    <Compile Include="SimplifyNullCheck\CSharpSimplifyNullCheckDiagnosticAnalyzer.cs" />
     <Compile Include="Structure\CSharpBlockStructureProvider.cs" />
     <Compile Include="Structure\CSharpStructureHelpers.cs" />
     <Compile Include="Structure\CSharpBlockStructureService.cs" />

src/Features/CSharp/Portable/SimplifyNullCheck/CSharpSimplifyNullCheckDiagnosticAnalyzer.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.SimplifyNullCheck;
+
+namespace Microsoft.CodeAnalysis.CSharp.SimplifyNullCheck
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    internal class CSharpSimplifyNullCheckDiagnosticAnalyzer : AbstractSimplifyNullCheckDiagnosticAnalyzer
+    {
+        protected override bool IsSupported(ParseOptions options)
+        {
+            var csOptions = (CSharpParseOptions)options;
+            return csOptions.LanguageVersion >= LanguageVersion.CSharp7;
+        }
+    }
+}
\ No newline at end of file

src/Features/Core/Portable/Features.csproj

@@ -92,7 +92,7 @@
     </Compile>
     <Compile Include="AddMissingReference\AbstractAddMissingReferenceCodeFixProvider.cs" />
     <Compile Include="AddMissingReference\CodeAction.cs" />
-    <Compile Include="SimplifyNullCheck\SimplifyNullCheckAnalyzer.cs" />
+    <Compile Include="SimplifyNullCheck\AbstractSimplifyNullCheckDiagnosticAnalyzer.cs" />
     <Compile Include="SimplifyNullCheck\SimplifyNullCheckCodeFixProvider.cs" />
     <Compile Include="Structure\BlockTypes.cs" />
     <Compile Include="CodeLens\CodeLensReferencesServiceFactory.cs" />

src/Features/Core/Portable/SimplifyNullCheck/SimplifyNullCheckAnalyzer.cs → src/Features/Core/Portable/SimplifyNullCheck/AbstractSimplifyNullCheckDiagnosticAnalyzer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Collections.Immutable;
-using System.Linq;
 using System.Reflection;
-using System.Text;
 using System.Threading;
-using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.Semantics;
 
@@ -32,8 +28,7 @@ namespace Microsoft.CodeAnalysis.SimplifyNullCheck
     /// Note: this analyzer can be udpated to run on VB once VB supports 'throw' 
     /// expressions as well.
     /// </summary>
-    [DiagnosticAnalyzer(LanguageNames.CSharp)]
-    internal class SimplifyNullCheckAnalyzer : DiagnosticAnalyzer, IBuiltInAnalyzer
+    internal abstract class AbstractSimplifyNullCheckDiagnosticAnalyzer : DiagnosticAnalyzer, IBuiltInAnalyzer
     {
         private static readonly LocalizableString s_localizableTitle = new LocalizableResourceString(nameof(FeaturesResources.Simplify_null_check), FeaturesResources.ResourceManager, typeof(FeaturesResources));
         private static readonly LocalizableString s_localizableMessage = new LocalizableResourceString(nameof(FeaturesResources.Simplify_null_check), WorkspacesResources.ResourceManager, typeof(WorkspacesResources));
@@ -60,6 +55,8 @@ public DiagnosticAnalyzerCategory GetAnalyzerCategory()
         private static MethodInfo s_getOperationInfo =
             typeof(SemanticModel).GetTypeInfo().GetDeclaredMethod("GetOperationInternal");
 
+        protected abstract bool IsSupported(ParseOptions options);
+
         public override void Initialize(AnalysisContext context)
         {
             s_registerOperationActionInfo.Invoke(context, new object[]
@@ -69,14 +66,19 @@ public override void Initialize(AnalysisContext context)
             });
         }
 
-        private void AnalyzeOperation(OperationAnalysisContext operationContext)
+        private void AnalyzeOperation(OperationAnalysisContext context)
         {
-            var cancellationToken = operationContext.CancellationToken;
+            if (!IsSupported(context.Operation.Syntax.SyntaxTree.Options))
+            {
+                return;
+            }
+
+            var cancellationToken = context.CancellationToken;
 
-            var throwOperation = (IThrowStatement)operationContext.Operation;
+            var throwOperation = (IThrowStatement)context.Operation;
             var throwStatement = throwOperation.Syntax;
 
-            var compilation = operationContext.Compilation;
+            var compilation = context.Compilation;
             var semanticModel = compilation.GetSemanticModel(throwStatement.SyntaxTree);
 
             var ifOperation = GetContainingIfOperation(
@@ -127,9 +129,9 @@ private void AnalyzeOperation(OperationAnalysisContext operationContext)
                 throwOperation.ThrownObject.Syntax.GetLocation(),
                 assignmentExpression.Value.Syntax.GetLocation());
 
-            operationContext.ReportDiagnostic(
+            context.ReportDiagnostic(
                 Diagnostic.Create(s_descriptor, ifOperation.Syntax.GetLocation(), additionalLocations: allLocations));
-            operationContext.ReportDiagnostic(
+            context.ReportDiagnostic(
                 Diagnostic.Create(s_descriptor, expressionStatement.Syntax.GetLocation(), additionalLocations: allLocations));
         }
 

src/Features/Core/Portable/SimplifyNullCheck/SimplifyNullCheckCodeFixProvider.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Composition;
 using System.Linq;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.CodeActions;

src/Workspaces/CSharp/Portable/CodeGeneration/CSharpSyntaxGenerator.cs

@@ -3478,6 +3478,11 @@ public override SyntaxNode ThrowStatement(SyntaxNode expressionOpt = null)
             return SyntaxFactory.ThrowStatement((ExpressionSyntax)expressionOpt);
         }
 
+        public override SyntaxNode ThrowExpression(SyntaxNode expression)
+        {
+            return SyntaxFactory.ThrowExpression((ExpressionSyntax)expression);
+        }
+
         public override SyntaxNode IfStatement(SyntaxNode condition, IEnumerable<SyntaxNode> trueStatements, IEnumerable<SyntaxNode> falseStatements = null)
         {
             if (falseStatements == null)

src/Workspaces/Core/Portable/Editing/SyntaxGenerator.cs

@@ -1302,6 +1302,11 @@ protected static SyntaxList<TNode> RemoveRange<TNode>(SyntaxList<TNode> list, in
         /// <param name="expression">An optional expression that can be thrown.</param>
         public abstract SyntaxNode ThrowStatement(SyntaxNode expression = null);
 
+        /// <summary>
+        /// Creates an expression that can be used to throw an exception.
+        /// </summary>
+        public abstract SyntaxNode ThrowExpression(SyntaxNode expression);
+
         /// <summary>
         /// Creates a statement that declares a single local variable.
         /// </summary>

src/Workspaces/Core/Portable/PublicAPI.Unshipped.txt

@@ -27,9 +27,9 @@ Microsoft.CodeAnalysis.Options.DocumentOptionSet.GetOption<T>(Microsoft.CodeAnal
 Microsoft.CodeAnalysis.Options.IOption.StorageLocations.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Options.OptionStorageLocation>
 Microsoft.CodeAnalysis.Options.Option<T>.Option(string feature, string name, T defaultValue, params Microsoft.CodeAnalysis.Options.OptionStorageLocation[] storageLocations) -> void
 Microsoft.CodeAnalysis.Options.Option<T>.StorageLocations.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Options.OptionStorageLocation>
+Microsoft.CodeAnalysis.Options.OptionSet.OptionSet() -> void
 Microsoft.CodeAnalysis.Options.OptionStorageLocation
 Microsoft.CodeAnalysis.Options.OptionStorageLocation.OptionStorageLocation() -> void
-Microsoft.CodeAnalysis.Options.OptionSet.OptionSet() -> void
 Microsoft.CodeAnalysis.Options.PerLanguageOption<T>.PerLanguageOption(string feature, string name, T defaultValue, params Microsoft.CodeAnalysis.Options.OptionStorageLocation[] storageLocations) -> void
 Microsoft.CodeAnalysis.Options.PerLanguageOption<T>.StorageLocations.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Options.OptionStorageLocation>
 Microsoft.CodeAnalysis.Solution.Options.get -> Microsoft.CodeAnalysis.Options.OptionSet
@@ -37,6 +37,7 @@ Microsoft.CodeAnalysis.Workspace.DocumentActiveContextChanged -> System.EventHan
 Microsoft.CodeAnalysis.Workspace.RaiseDocumentActiveContextChangedEventAsync(Microsoft.CodeAnalysis.Text.SourceTextContainer sourceTextContainer, Microsoft.CodeAnalysis.DocumentId oldActiveContextDocumentId, Microsoft.CodeAnalysis.DocumentId newActiveContextDocumentId) -> System.Threading.Tasks.Task
 abstract Microsoft.CodeAnalysis.Editing.SyntaxGenerator.GetSwitchSections(Microsoft.CodeAnalysis.SyntaxNode switchStatement) -> System.Collections.Generic.IReadOnlyList<Microsoft.CodeAnalysis.SyntaxNode>
 abstract Microsoft.CodeAnalysis.Editing.SyntaxGenerator.InsertSwitchSections(Microsoft.CodeAnalysis.SyntaxNode switchStatement, int index, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.SyntaxNode> switchSections) -> Microsoft.CodeAnalysis.SyntaxNode
+abstract Microsoft.CodeAnalysis.Editing.SyntaxGenerator.ThrowExpression(Microsoft.CodeAnalysis.SyntaxNode expression) -> Microsoft.CodeAnalysis.SyntaxNode
 override Microsoft.CodeAnalysis.CodeStyle.CodeStyleOption<T>.Equals(object obj) -> bool
 override Microsoft.CodeAnalysis.CodeStyle.CodeStyleOption<T>.GetHashCode() -> int
 override Microsoft.CodeAnalysis.CodeStyle.NotificationOption.ToString() -> string

src/Workspaces/VisualBasic/Portable/CodeGeneration/VisualBasicSyntaxGenerator.vb

@@ -276,6 +276,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeGeneration
             Return SyntaxFactory.ThrowStatement(DirectCast(expressionOpt, ExpressionSyntax))
         End Function
 
+        Public Overrides Function ThrowExpression(expression As SyntaxNode) As SyntaxNode
+            Throw New NotSupportedException("ThrowExpressions are not supported in Visual Basic")
+        End Function
+
         Public Overrides Function TypeExpression(typeSymbol As ITypeSymbol) As SyntaxNode
             Return typeSymbol.GenerateTypeSyntax()
         End Function