If you apply `wait=yes` and use `instance_tags` as your filter for
stopping/starting EC2 instances, this stack trace happens:
```
An exception occurred during task execution. The full traceback is: │~
Traceback (most recent call last): │~
File "/tmp/ryansb/ansible_FwE8VR/ansible_module_ec2.py", line 1540, in <module> │~
main() │~
File "/tmp/ryansb/ansible_FwE8VR/ansible_module_ec2.py", line 1514, in main │~
(changed, instance_dict_array, new_instance_ids) = startstop_instances(module, ec2, instance_ids, state, instance_tags) │~
File "/tmp/ryansb/ansible_FwE8VR/ansible_module_ec2.py", line 1343, in startstop_instances │~
if len(matched_instances) < len(instance_ids): │~
TypeError: object of type 'NoneType' has no len() │~
│~
fatal: [localhost -> localhost]: FAILED! => {"changed": false, "failed": true, "invocation": {"module_name": "ec2"}, "module_stderr": "Traceb│~
ack (most recent call last):\n File \"/tmp/ryansb/ansible_FwE8VR/ansible_module_ec2.py\", line 1540, in <module>\n main()\n File \"/tmp/│~
ryansb/ansible_FwE8VR/ansible_module_ec2.py\", line 1514, in main\n (changed, instance_dict_array, new_instance_ids) = startstop_instances│~
(module, ec2, instance_ids, state, instance_tags)\n File \"/tmp/ryansb/ansible_FwE8VR/ansible_module_ec2.py\", line 1343, in startstop_insta│~
nces\n if len(matched_instances) < len(instance_ids):\nTypeError: object of type 'NoneType' has no len()\n", "module_stdout": "", "msg": "│~
MODULE FAILURE", "parsed": false}
```
That's because the `instance_ids` variable is None if not supplied
in the task. That means the instances that result from the instance_tags
query aren't going to be included in the wait loop. To fix this, a list
needs to be kept of instances with matching tags and that list needs to
be added to `instance_ids` before the wait loop.
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