# Buggy code
def main():
    argument_spec = ec2_argument_spec()
    argument_spec.update(
        dict(
            subnet_ids=dict(type="list", default=[]),
            filters=dict(type="dict", default={}),
        )
    )

    module = AnsibleModule(argument_spec=argument_spec, supports_check_mode=True)

    if not HAS_BOTO3:
        module.fail_json(msg="boto3 is required for this module")

    region, ec2_url, aws_connect_params = get_aws_connection_info(module, boto3=True)

    try:
        connection = boto3_conn(
            module, conn_type="client", resource="ec2", **aws_connect_params
        )
    except (
        botocore.exceptions.NoCredentialsError,
        botocore.exceptions.ProfileNotFound,
    ) as e:
        module.fail_json(
            msg=e.message,
            exception=traceback.format_exc(),
            **camel_dict_to_snake_dict(e.response),
        )

    describe_subnets(connection, module)


# Traceback (botocore.exceptions.NoRegionError)
The full traceback is:
Traceback (most recent call last):
File "/var/folders/0j/0s0tft6575s6c3dxwvmjy1w40000gn/T/ansible_2Z1Z5m/ansible_module_ec2_vpc_subnet_facts.py", line 248, in <module>
main()
File "/var/folders/0j/0s0tft6575s6c3dxwvmjy1w40000gn/T/ansible_2Z1Z5m/ansible_module_ec2_vpc_subnet_facts.py", line 240, in main
connection = boto3_conn(module, conn_type='client', resource='ec2', **aws_connect_params)
File "/var/folders/0j/0s0tft6575s6c3dxwvmjy1w40000gn/T/ansible_2Z1Z5m/ansible_modlib.zip/ansible/module_utils/ec2.py", line 100, in boto3_conn
File "/var/folders/0j/0s0tft6575s6c3dxwvmjy1w40000gn/T/ansible_2Z1Z5m/ansible_modlib.zip/ansible/module_utils/ec2.py", line 119, in _boto3_conn
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/boto3/session.py", line 263, in client
aws_session_token=aws_session_token, config=config)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/session.py", line 836, in create_client
client_config=config, api_version=api_version)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/client.py", line 71, in create_client
verify, credentials, scoped_config, client_config, endpoint_bridge)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/client.py", line 283, in _get_client_args
verify, credentials, scoped_config, client_config, endpoint_bridge)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/args.py", line 45, in get_client_args
endpoint_url, is_secure, scoped_config)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/args.py", line 111, in compute_client_args
service_name, region_name, endpoint_url, is_secure)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/client.py", line 356, in resolve
service_name, region_name)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/regions.py", line 122, in construct_endpoint
partition, service_name, region_name)
File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/botocore/regions.py", line 135, in _endpoint_for_partition
raise NoRegionError()
botocore.exceptions.NoRegionError: You must specify a region.

# Fixed code
def main():
    argument_spec = ec2_argument_spec()
    argument_spec.update(
        dict(
            subnet_ids=dict(type="list", default=[]),
            filters=dict(type="dict", default={}),
        )
    )

    module = AnsibleModule(argument_spec=argument_spec, supports_check_mode=True)

    if not HAS_BOTO3:
        module.fail_json(msg="boto3 is required for this module")

    region, ec2_url, aws_connect_params = get_aws_connection_info(module, boto3=True)

    try:
        connection = boto3_conn(
            module,
            conn_type="client",
            resource="ec2",
            region=region,
            endpoint=ec2_url,
            **aws_connect_params,
        )
    except (
        botocore.exceptions.NoCredentialsError,
        botocore.exceptions.ProfileNotFound,
    ) as e:
        module.fail_json(
            msg=e.message,
            exception=traceback.format_exc(),
            **camel_dict_to_snake_dict(e.response),
        )

    describe_subnets(connection, module)