allow default attribute constructor to take no args

EventGridBinding/Function.cs

@@ -6,7 +6,7 @@ namespace EventGridBinding
 {
     public static class Function
     {
-        public static void testEventGrid([EventGridTrigger("eventhubarchive")] EventGridEvent value)
+        public static void testEventGrid([EventGridTrigger] EventGridEvent value)
         {
             Console.WriteLine(value);
         }

EventGridExtension/EventGridTriggerAttribute.cs

@@ -11,6 +11,11 @@ namespace Microsoft.Azure.WebJobs
     public sealed class EventGridTriggerAttribute : Attribute
     {
         public const string eventHubArchive = "eventHubArchive";
+        public EventGridTriggerAttribute()
+        {
+            Publisher = null; // if this is not provided, only EventGridEvent can be parsed
+        }
+
         public EventGridTriggerAttribute(string publisher)
         {
             // FIXME

EventGridExtension/EventGridTriggerAttributeBindingProvider.cs

@@ -40,18 +40,20 @@ namespace Microsoft.Azure.WebJobs
                 return Task.FromResult<ITriggerBinding>(null);
             }
 
-            if (parameter.ParameterType == typeof(EventGridEvent))
-            {
-                // universally supported
-                return Task.FromResult<ITriggerBinding>(new EventGridTriggerBinding(context.Parameter, _extensionConfigProvider, context.Parameter.Member.Name));
-            }
-
             // depends on the publisher, we could have different expectation for paramter
             string publisher = attribute.Publisher;
-            if (publisher == EventGridTriggerAttribute.eventHubArchive && parameter.ParameterType != typeof(Stream))
+            if (String.IsNullOrEmpty(publisher) && !(parameter.ParameterType == typeof(EventGridEvent)))
+            {
+                throw new InvalidOperationException($"Can only bind EventGridTriggerAttribute to type 'EventGridEvent' when no publisher is specified.");
+            }
+            else if (parameter.ParameterType == typeof(EventGridEvent))
+            {
+                // always valid, no need to check for publisher and what the specify parameter publisher can parse to
+            }
+            else if (publisher == EventGridTriggerAttribute.eventHubArchive && parameter.ParameterType != typeof(Stream))
             {
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
-                    "Can't bind EventGridTriggerAttribute to type '{0}'.", parameter.ParameterType));
+                    "Can't bind EventGridTriggerAttribute with publisher '{0}' to type '{1}'.", publisher, parameter.ParameterType));
             }
             // unsupported publisher is caught in attribute constrcutor
             return Task.FromResult<ITriggerBinding>(new EventGridTriggerBinding(context.Parameter, _extensionConfigProvider, context.Parameter.Member.Name, publisher));
@@ -68,7 +70,7 @@ namespace Microsoft.Azure.WebJobs
             private object _value;
             private readonly string _publisher;
 
-            public EventGridTriggerBinding(ParameterInfo parameter, EventGridExtensionConfig listenersStore, string functionName, string publisher = null)
+            public EventGridTriggerBinding(ParameterInfo parameter, EventGridExtensionConfig listenersStore, string functionName, string publisher)
             {
                 _publisher = publisher;
                 _listenersStore = listenersStore;