[CodeActions] Don't crash on null accessors in ValueParameterUnusedIssue.

ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ValueParameterUnusedIssue.cs

@@ -24,7 +24,6 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 using System.Collections.Generic;
-using ICSharpCode.NRefactory.Semantics;
 using System.Linq;
 using ICSharpCode.NRefactory.TypeSystem;
 using ICSharpCode.NRefactory.CSharp.Resolver;
@@ -59,9 +58,7 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 
 			public override void VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration)
 			{
-				var body = propertyDeclaration.Setter.Body;
-				if (!body.IsNull)
-					FindIssuesInNode(propertyDeclaration.Setter, body);
+				FindIssuesInNode(propertyDeclaration.Setter, propertyDeclaration.Setter.Body);
 			}
 
 			public override void VisitCustomEventDeclaration(CustomEventDeclaration eventDeclaration)
@@ -82,6 +79,8 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 
 			void FindIssuesInNode(AstNode anchor, AstNode node, string accessorName = "setter")
 			{
+				if (node == null || node.IsNull)
+					return;
 				var variable = context.GetResolverStateBefore(node).LocalVariables
 					.Where(v => v.Name == "value").FirstOrDefault();
 				if (variable == null)

ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/ValueParameterUnusedTests.cs

@@ -117,13 +117,25 @@ namespace ICSharpCode.NRefactory.CSharp.CodeIssues
 			var issues = GetIssues(new ValueParameterUnusedIssue(), input, out context);
 			Assert.AreEqual(0, issues.Count);
 		}
-
+		
 		[Test]
 		public void IgnoreReadOnlyProperty()
 		{
 			var input = @"class A
 {
-	string  Property { get; }
+string  Property { get; }
+}";
+			TestRefactoringContext context;
+			var issues = GetIssues(new ValueParameterUnusedIssue(), input, out context);
+			Assert.AreEqual(0, issues.Count);
+		}
+		
+		[Test]
+		public void DoesNotCrashOnNullIndexerAccessorBody()
+		{
+			var input = @"abstract class A
+{
+public abstract string this[int i] { get; set; }
 }";
 			TestRefactoringContext context;
 			var issues = GetIssues(new ValueParameterUnusedIssue(), input, out context);