Webhooks: default tracking event tags=[], metadata={}

If a tracking event doesn't contain tags or metadata, set the event
record fields to tags=[] or metadata={} to simplify checking values.

Closes #67

anymail/webhooks/mailgun.py

@@ -113,7 +113,7 @@ class MailgunTrackingWebhookView(MailgunBaseWebhookView):
         try:
             headers = json.loads(esp_event['message-headers'])
         except (KeyError, ):
-            metadata = None
+            metadata = {}
         else:
             variables = [value for [field, value] in headers
                          if field == 'X-Mailgun-Variables']
@@ -121,10 +121,10 @@ class MailgunTrackingWebhookView(MailgunBaseWebhookView):
                 # Each X-Mailgun-Variables value is JSON. Parse and merge them all into single dict:
                 metadata = combine(*[json.loads(value) for value in variables])
             else:
-                metadata = None
+                metadata = {}
 
         # tags are sometimes delivered as X-Mailgun-Tag fields, sometimes as tag
-        tags = esp_event.getlist('tag', esp_event.getlist('X-Mailgun-Tag', None))
+        tags = esp_event.getlist('tag', esp_event.getlist('X-Mailgun-Tag', []))
 
         return AnymailTrackingEvent(
             event_type=event_type,

anymail/webhooks/mandrill.py

@@ -128,12 +128,12 @@ class MandrillTrackingWebhookView(MandrillBaseWebhookView):
         try:
             metadata = esp_event['msg']['metadata']
         except KeyError:
-            metadata = None
+            metadata = {}
 
         try:
             tags = esp_event['msg']['tags']
         except KeyError:
-            tags = None
+            tags = []
 
         return AnymailTrackingEvent(
             click_url=esp_event.get('url', None),

anymail/webhooks/postmark.py

@@ -89,7 +89,7 @@ class PostmarkTrackingWebhookView(PostmarkBaseWebhookView):
         try:
             tags = [esp_event['Tag']]
         except KeyError:
-            tags = None
+            tags = []
 
         return AnymailTrackingEvent(
             description=esp_event.get('Description', None),

anymail/webhooks/sendgrid.py

@@ -72,7 +72,7 @@ class SendGridTrackingWebhookView(SendGridBaseWebhookView):
         if len(metadata_keys) > 0:
             metadata = {key: esp_event[key] for key in metadata_keys}
         else:
-            metadata = None
+            metadata = {}
 
         return AnymailTrackingEvent(
             event_type=event_type,
@@ -82,7 +82,7 @@ class SendGridTrackingWebhookView(SendGridBaseWebhookView):
             recipient=esp_event.get('email', None),
             reject_reason=reject_reason,
             mta_response=mta_response,
-            tags=esp_event.get('category', None),
+            tags=esp_event.get('category', []),
             metadata=metadata,
             click_url=esp_event.get('url', None),
             user_agent=esp_event.get('useragent', None),

anymail/webhooks/sparkpost.py

@@ -108,7 +108,7 @@ class SparkPostTrackingWebhookView(SparkPostBaseWebhookView):
             tag = event['campaign_id']  # not 'rcpt_tags' -- those don't come from sending a message
             tags = [tag] if tag else None
         except KeyError:
-            tags = None
+            tags = []
 
         try:
             reject_reason = self.reject_reasons.get(event['bounce_class'], RejectReason.OTHER)
@@ -129,7 +129,7 @@ class SparkPostTrackingWebhookView(SparkPostBaseWebhookView):
             mta_response=event.get('raw_reason', None),
             # description=???,
             tags=tags,
-            metadata=event.get('rcpt_meta', None) or None,  # message + recipient metadata
+            metadata=event.get('rcpt_meta', None) or {},  # message + recipient metadata
             click_url=event.get('target_link_url', None),
             user_agent=event.get('user_agent', None),
             esp_event=raw_event,