prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Validation error in CodeCommit Trigger
  It appears that the validation for the CodeCommit Trigger class does not currently allow the use of any intrinsic functions for the `Events` property, and only accepts a list of hard coded values.
  
  https://github.com/cloudtools/troposphere/blob/45582eb1d21a6cc9cfa608f626d8acbf0317f37f/troposphere/codecommit.py#L18-L32
  
  We are trying to allow for the dynamic selection of  the values with a  parameter, but encounter errors when attempting to use a `Ref`.  A snippet of our trigger definition, and the error encountered is below:
  
  ```
  repo_trigger1 = codecommit.Trigger(
              Name = Ref(trigger_1_name),
              CustomData = Ref(trigger_1_custom_data),
              DestinationArn = Ref(trigger_1_destination_arn),
              Branches = Ref(trigger_1_branches),
              Events = Ref(trigger_1_events),
          )
  ```
  We are able to successfully generate the template when changing the `Events` assignment to:
  
  ```Events = ["all"],```
  
  I believe we just need to check if the value is one of the Helper functions before iterating through the events.  I will try to get a fix pushed up for review.
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `troposphere/codecommit.py`
  Content:
  ```
  1 # Copyright (c) 2016, Mark Peek <mark@peek.org>
  2 # All rights reserved.
  3 #
  4 # See LICENSE file for full license.
  5 
  6 from . import AWSObject, AWSProperty
  7 
  8 
  9 class Trigger(AWSProperty):
  10     props = {
  11         'Branches': ([basestring], False),
  12         'CustomData': (basestring, False),
  13         'DestinationArn': (basestring, False),
  14         'Events': ([basestring], False),
  15         'Name': (basestring, False),
  16     }
  17 
  18     def validate(self):
  19         valid = [
  20             'all',
  21             'createReference',
  22             'deleteReference',
  23             'updateReference',
  24         ]
  25         events = self.properties.get('Events')
  26         if events:
  27             if 'all' in events and len(events) != 1:
  28                 raise ValueError('Trigger events: all must be used alone')
  29             else:
  30                 for e in events:
  31                     if e not in valid:
  32                         raise ValueError('Trigger: invalid event %s' % e)
  33 
  34 
  35 class Repository(AWSObject):
  36     resource_type = "AWS::CodeCommit::Repository"
  37 
  38     props = {
  39         'RepositoryDescription': (basestring, False),
  40         'RepositoryName': (basestring, True),
  41         'Triggers': ([Trigger], False),
  42     }
  43
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/troposphere/codecommit.py b/troposphere/codecommit.py
  --- a/troposphere/codecommit.py
  +++ b/troposphere/codecommit.py
  @@ -3,7 +3,7 @@
   #
   # See LICENSE file for full license.
   
  -from . import AWSObject, AWSProperty
  +from . import AWSHelperFn, AWSObject, AWSProperty
   
   
   class Trigger(AWSProperty):
  @@ -23,12 +23,12 @@
               'updateReference',
           ]
           events = self.properties.get('Events')
  -        if events:
  +        if events and not isinstance(events, AWSHelperFn):
               if 'all' in events and len(events) != 1:
                   raise ValueError('Trigger events: all must be used alone')
               else:
                   for e in events:
  -                    if e not in valid:
  +                    if e not in valid and not isinstance(e, AWSHelperFn):
                           raise ValueError('Trigger: invalid event %s' % e)
  
verification_info: {"golden_diff": "diff --git a/troposphere/codecommit.py b/troposphere/codecommit.py\n--- a/troposphere/codecommit.py\n+++ b/troposphere/codecommit.py\n@@ -3,7 +3,7 @@\n #\n # See LICENSE file for full license.\n \n-from . import AWSObject, AWSProperty\n+from . import AWSHelperFn, AWSObject, AWSProperty\n \n \n class Trigger(AWSProperty):\n@@ -23,12 +23,12 @@\n             'updateReference',\n         ]\n         events = self.properties.get('Events')\n-        if events:\n+        if events and not isinstance(events, AWSHelperFn):\n             if 'all' in events and len(events) != 1:\n                 raise ValueError('Trigger events: all must be used alone')\n             else:\n                 for e in events:\n-                    if e not in valid:\n+                    if e not in valid and not isinstance(e, AWSHelperFn):\n                         raise ValueError('Trigger: invalid event %s' % e)\n", "issue": "Validation error in CodeCommit Trigger\nIt appears that the validation for the CodeCommit Trigger class does not currently allow the use of any intrinsic functions for the `Events` property, and only accepts a list of hard coded values.\r\n\r\nhttps://github.com/cloudtools/troposphere/blob/45582eb1d21a6cc9cfa608f626d8acbf0317f37f/troposphere/codecommit.py#L18-L32\r\n\r\nWe are trying to allow for the dynamic selection of  the values with a  parameter, but encounter errors when attempting to use a `Ref`.  A snippet of our trigger definition, and the error encountered is below:\r\n\r\n```\r\nrepo_trigger1 = codecommit.Trigger(\r\n            Name = Ref(trigger_1_name),\r\n            CustomData = Ref(trigger_1_custom_data),\r\n            DestinationArn = Ref(trigger_1_destination_arn),\r\n            Branches = Ref(trigger_1_branches),\r\n            Events = Ref(trigger_1_events),\r\n        )\r\n```\r\nWe are able to successfully generate the template when changing the `Events` assignment to:\r\n\r\n```Events = [\"all\"],```\r\n\r\nI believe we just need to check if the value is one of the Helper functions before iterating through the events.  I will try to get a fix pushed up for review.\n", "before_files": [{"content": "# Copyright (c) 2016, Mark Peek <mark@peek.org>\n# All rights reserved.\n#\n# See LICENSE file for full license.\n\nfrom . import AWSObject, AWSProperty\n\n\nclass Trigger(AWSProperty):\n    props = {\n        'Branches': ([basestring], False),\n        'CustomData': (basestring, False),\n        'DestinationArn': (basestring, False),\n        'Events': ([basestring], False),\n        'Name': (basestring, False),\n    }\n\n    def validate(self):\n        valid = [\n            'all',\n            'createReference',\n            'deleteReference',\n            'updateReference',\n        ]\n        events = self.properties.get('Events')\n        if events:\n            if 'all' in events and len(events) != 1:\n                raise ValueError('Trigger events: all must be used alone')\n            else:\n                for e in events:\n                    if e not in valid:\n                        raise ValueError('Trigger: invalid event %s' % e)\n\n\nclass Repository(AWSObject):\n    resource_type = \"AWS::CodeCommit::Repository\"\n\n    props = {\n        'RepositoryDescription': (basestring, False),\n        'RepositoryName': (basestring, True),\n        'Triggers': ([Trigger], False),\n    }\n", "path": "troposphere/codecommit.py"}], "after_files": [{"content": "# Copyright (c) 2016, Mark Peek <mark@peek.org>\n# All rights reserved.\n#\n# See LICENSE file for full license.\n\nfrom . import AWSHelperFn, AWSObject, AWSProperty\n\n\nclass Trigger(AWSProperty):\n    props = {\n        'Branches': ([basestring], False),\n        'CustomData': (basestring, False),\n        'DestinationArn': (basestring, False),\n        'Events': ([basestring], False),\n        'Name': (basestring, False),\n    }\n\n    def validate(self):\n        valid = [\n            'all',\n            'createReference',\n            'deleteReference',\n            'updateReference',\n        ]\n        events = self.properties.get('Events')\n        if events and not isinstance(events, AWSHelperFn):\n            if 'all' in events and len(events) != 1:\n                raise ValueError('Trigger events: all must be used alone')\n            else:\n                for e in events:\n                    if e not in valid and not isinstance(e, AWSHelperFn):\n                        raise ValueError('Trigger: invalid event %s' % e)\n\n\nclass Repository(AWSObject):\n    resource_type = \"AWS::CodeCommit::Repository\"\n\n    props = {\n        'RepositoryDescription': (basestring, False),\n        'RepositoryName': (basestring, True),\n        'Triggers': ([Trigger], False),\n    }\n", "path": "troposphere/codecommit.py"}]}