Fixed failing tests.

src/Markup/Perspex.Markup/Data/IndexerNode.cs

@@ -53,6 +53,10 @@ namespace Perspex.Markup.Data
         private void IndexerPropertyChanged(object sender, PropertyChangedEventArgs e)
         {
             var typeInfo = sender.GetType().GetTypeInfo();
+            if (typeInfo.GetDeclaredProperty(e.PropertyName) == null)
+            {
+                return;
+            }
             if (typeInfo.GetDeclaredProperty(e.PropertyName).GetIndexParameters().Any())
             {
                 CurrentValue = GetValue(sender);

src/Markup/Perspex.Markup/Data/Parsers/ArgumentListParser.cs

@@ -32,6 +32,10 @@ namespace Perspex.Markup.Data.Parsers
                         {
                             builder.Append(r.Take());
                         }
+                        if (builder.Length == 0)
+                        {
+                            throw new ExpressionParseException(r.Position, "Expected indexer argument.");
+                        }
                         result.Add(builder.ToString());
                     }