diff --git a/moto/swf/models/workflow_execution.py b/moto/swf/models/workflow_execution.py
index df75a99b8..b0e6427cd 100644
--- a/moto/swf/models/workflow_execution.py
+++ b/moto/swf/models/workflow_execution.py
@@ -200,6 +200,9 @@ class WorkflowExecution(object):
         dt.start(evt.event_id)
 
     def complete_decision_task(self, task_token, decisions=None, execution_context=None):
+        # 'decisions' can be None per boto.swf defaults, so replace it with something iterable
+        if not decisions:
+            decisions = []
         # In case of a malformed or invalid decision task, SWF will raise an error and
         # it won't perform any of the decisions in the decision set.
         self.validate_decisions(decisions)
@@ -236,9 +239,6 @@ class WorkflowExecution(object):
         validation problem, such as a malformed decision for instance. I didn't
         find an explicit documentation for that though, so criticisms welcome.
         """
-        if not decisions:
-            return
-
         problems = []
 
         # check close decision is last
@@ -285,10 +285,6 @@ class WorkflowExecution(object):
         Handles a Decision according to SWF docs.
         See: http://docs.aws.amazon.com/amazonswf/latest/apireference/API_Decision.html
         """
-        # 'decisions' can be None per boto.swf defaults, so replace it with something iterable
-        if not decisions:
-            decisions = []
-
         # handle each decision separately, in order
         for decision in decisions:
             decision_type = decision["decisionType"]
@@ -339,6 +335,17 @@ class WorkflowExecution(object):
         )
 
     def schedule_activity_task(self, event_id, attributes):
+        # Helper function to avoid repeating ourselves in the next sections
+        def fail_schedule_activity_task(_type, _cause):
+            self._add_event(
+                "ScheduleActivityTaskFailed",
+                activity_id=attributes["activityId"],
+                activity_type=_type,
+                cause=_cause,
+                decision_task_completed_event_id=event_id,
+            )
+            self.should_schedule_decision_next = True
+
         activity_type = self.domain.get_type(
             "activity",
             attributes["activityType"]["name"],
@@ -348,35 +355,16 @@ class WorkflowExecution(object):
         if not activity_type:
             fake_type = ActivityType(attributes["activityType"]["name"],
                                      attributes["activityType"]["version"])
-            self._add_event(
-                "ScheduleActivityTaskFailed",
-                activity_id=attributes["activityId"],
-                activity_type=fake_type,
-                cause="ACTIVITY_TYPE_DOES_NOT_EXIST",
-                decision_task_completed_event_id=event_id,
-            )
-            self.should_schedule_decision_next = True
+            fail_schedule_activity_task(fake_type,
+                                        "ACTIVITY_TYPE_DOES_NOT_EXIST")
             return
         if activity_type.status == "DEPRECATED":
-            self._add_event(
-                "ScheduleActivityTaskFailed",
-                activity_id=attributes["activityId"],
-                activity_type=activity_type,
-                cause="ACTIVITY_TYPE_DEPRECATED",
-                decision_task_completed_event_id=event_id,
-            )
-            self.should_schedule_decision_next = True
+            fail_schedule_activity_task(activity_type,
+                                        "ACTIVITY_TYPE_DEPRECATED")
             return
-        if any(at for at in self.activity_tasks
-               if at.activity_id == attributes["activityId"]):
-            self._add_event(
-                "ScheduleActivityTaskFailed",
-                activity_id=attributes["activityId"],
-                activity_type=activity_type,
-                cause="ACTIVITY_ID_ALREADY_IN_USE",
-                decision_task_completed_event_id=event_id,
-            )
-            self.should_schedule_decision_next = True
+        if any(at for at in self.activity_tasks if at.activity_id == attributes["activityId"]):
+            fail_schedule_activity_task(activity_type,
+                                        "ACTIVITY_ID_ALREADY_IN_USE")
             return
 
         # find task list or default task list, else fail
@@ -384,14 +372,8 @@ class WorkflowExecution(object):
         if not task_list and activity_type.task_list:
             task_list = activity_type.task_list
         if not task_list:
-            self._add_event(
-                "ScheduleActivityTaskFailed",
-                activity_id=attributes["activityId"],
-                activity_type=activity_type,
-                cause="DEFAULT_TASK_LIST_UNDEFINED",
-                decision_task_completed_event_id=event_id,
-            )
-            self.should_schedule_decision_next = True
+            fail_schedule_activity_task(activity_type,
+                                        "DEFAULT_TASK_LIST_UNDEFINED")
             return
 
         # find timeouts or default timeout, else fail
@@ -402,14 +384,8 @@ class WorkflowExecution(object):
             timeouts[_type] = attributes.get(_type, default_value)
             if not timeouts[_type]:
                 error_key = default_key.replace("default_task_", "default_")
-                self._add_event(
-                    "ScheduleActivityTaskFailed",
-                    activity_id=attributes["activityId"],
-                    activity_type=activity_type,
-                    cause="{}_UNDEFINED".format(error_key.upper()),
-                    decision_task_completed_event_id=event_id,
-                )
-                self.should_schedule_decision_next = True
+                fail_schedule_activity_task(activity_type,
+                                            "{}_UNDEFINED".format(error_key.upper()))
                 return
 
         task = ActivityTask(