fix: Handle empty lists in TAXII status responses

These elements of the response are optional, so we should accept
situations when they aren't provided at all. This change simply checks
if the iterable `successes`, `pendings` and `failures` are truthy prior
to verifying that their lengths match the associated `*_count`
attribute. As such, we now accept status responses which return empty
lists for these elements as well as responses which omit them entirely.

Change-Id: I0ff802b9722c536144403a33e399c73fd29bdc61

taxii2client/v20/__init__.py

@@ -172,19 +172,19 @@ def _validate_status(self):
             msg = "No 'pending_count' in Status for request '{}'"
             raise ValidationError(msg.format(self.url))
 
-        if len(self.successes) != self.success_count:
+        if self.successes and len(self.successes) != self.success_count:
             msg = "Found successes={}, but success_count={} in status '{}'"
             raise ValidationError(msg.format(self.successes,
                                              self.success_count,
                                              self.id))
 
-        if len(self.pendings) != self.pending_count:
+        if self.pendings and len(self.pendings) != self.pending_count:
             msg = "Found pendings={}, but pending_count={} in status '{}'"
             raise ValidationError(msg.format(self.pendings,
                                              self.pending_count,
                                              self.id))
 
-        if len(self.failures) != self.failure_count:
+        if self.failures and len(self.failures) != self.failure_count:
             msg = "Found failures={}, but failure_count={} in status '{}'"
             raise ValidationError(msg.format(self.failures,
                                              self.failure_count,

taxii2client/v21/__init__.py

@@ -135,19 +135,19 @@ def _validate_status(self):
             msg = "No 'pending_count' in Status for request '{}'"
             raise ValidationError(msg.format(self.url))
 
-        if len(self.successes) != self.success_count:
+        if self.successes and len(self.successes) != self.success_count:
             msg = "Found successes={}, but success_count={} in status '{}'"
             raise ValidationError(msg.format(self.successes,
                                              self.success_count,
                                              self.id))
 
-        if len(self.pendings) != self.pending_count:
+        if self.pendings and len(self.pendings) != self.pending_count:
             msg = "Found pendings={}, but pending_count={} in status '{}'"
             raise ValidationError(msg.format(self.pendings,
                                              self.pending_count,
                                              self.id))
 
-        if len(self.failures) != self.failure_count:
+        if self.failures and len(self.failures) != self.failure_count:
             msg = "Found failures={}, but failure_count={} in status '{}'"
             raise ValidationError(msg.format(self.failures,
                                              self.failure_count,