# Buggy code
def main():
    argument_spec = ec2_argument_spec()
    argument_spec.update(
        dict(
            az=dict(default=None, required=False),
            cidr=dict(default=None, required=True),
            state=dict(default="present", choices=["present", "absent"]),
            tags=dict(
                default={}, required=False, type="dict", aliases=["resource_tags"]
            ),
            vpc_id=dict(default=None, required=True),
            map_public=dict(default=False, required=False, type="bool"),
        )
    )

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

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

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

    if region:
        connection = boto3_conn(
            module,
            conn_type="client",
            resource="ec2",
            region=region,
            endpoint=ec2_url,
            **aws_connect_params,
        )
    else:
        module.fail_json(msg="region must be specified")

    vpc_id = module.params.get("vpc_id")
    tags = module.params.get("tags")
    cidr = module.params.get("cidr")
    az = module.params.get("az")
    state = module.params.get("state")
    map_public = module.params.get("map_public")

    try:
        if state == "present":
            result = ensure_subnet_present(
                connection,
                module,
                vpc_id,
                cidr,
                az,
                tags,
                map_public,
                check_mode=module.check_mode,
            )
        elif state == "absent":
            result = ensure_subnet_absent(
                connection, module, vpc_id, cidr, check_mode=module.check_mode
            )
    except botocore.exceptions.ClientError as e:
        module.fail_json(
            msg=e.message,
            exception=traceback.format_exc(),
            **camel_dict_to_snake_dict(e.response),
        )

    module.exit_json(**result)


# Traceback (botocore.exceptions.ParamValidationError)
The full traceback is:
Traceback (most recent call last):
File "/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py", line 274, in <module>
main()
File "/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py", line 262, in main
check_mode=module.check_mode)
File "/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py", line 189, in ensure_subnet_present
subnet = create_subnet(conn, module, vpc_id, cidr, az, check_mode)
File "/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py", line 127, in create_subnet
new_subnet = get_subnet_info(conn.create_subnet(VpcId=vpc_id, CidrBlock=cidr, AvailabilityZone=az))
File "/usr/local/lib/python2.7/dist-packages/botocore/client.py", line 312, in _api_call
return self._make_api_call(operation_name, kwargs)
File "/usr/local/lib/python2.7/dist-packages/botocore/client.py", line 575, in _make_api_call
api_params, operation_model, context=request_context)
File "/usr/local/lib/python2.7/dist-packages/botocore/client.py", line 630, in _convert_to_request_dict
api_params, operation_model)
File "/usr/local/lib/python2.7/dist-packages/botocore/validate.py", line 291, in serialize_to_request
raise ParamValidationError(report=report.generate_report())
botocore.exceptions.ParamValidationError: Parameter validation failed:
Invalid type for parameter AvailabilityZone, value: None, type: <type 'NoneType'>, valid types: <type 'basestring'>

failed: [localhost] (item=10.10.0.0/24) => {
"changed": false,
"failed": true,
"item": "10.10.0.0/24",
"module_stderr": "Traceback (most recent call last):\n  File \"/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py\", line 274, in <module>\n    main()\n  File \"/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py\", line 262, in main\n    check_mode=module.check_mode)\n  File \"/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py\", line 189, in ensure_subnet_present\n    subnet = create_subnet(conn, module, vpc_id, cidr, az, check_mode)\n  File \"/tmp/ansible_jmC5F8/ansible_module_ec2_vpc_subnet.py\", line 127, in create_subnet\n    new_subnet = get_subnet_info(conn.create_subnet(VpcId=vpc_id, CidrBlock=cidr, AvailabilityZone=az))\n  File \"/usr/local/lib/python2.7/dist-packages/botocore/client.py\", line 312, in _api_call\n    return self._make_api_call(operation_name, kwargs)\n  File \"/usr/local/lib/python2.7/dist-packages/botocore/client.py\", line 575, in _make_api_call\n    api_params, operation_model, context=request_context)\n  File \"/usr/local/lib/python2.7/dist-packages/botocore/client.py\", line 630, in _convert_to_request_dict\n    api_params, operation_model)\n  File \"/usr/local/lib/python2.7/dist-packages/botocore/validate.py\", line 291, in serialize_to_request\n    raise ParamValidationError(report=report.generate_report())\nbotocore.exceptions.ParamValidationError: Parameter validation failed:\nInvalid type for parameter AvailabilityZone, value: None, type: <type 'NoneType'>, valid types: <type 'basestring'>\n",
"module_stdout": "",
"msg": "MODULE FAILURE",
"rc": 0
}

# Fixed code
def main():
    argument_spec = ec2_argument_spec()
    argument_spec.update(
        dict(
            az=dict(default=None, required=False),
            cidr=dict(default=None, required=True),
            state=dict(default="present", choices=["present", "absent"]),
            tags=dict(
                default={}, required=False, type="dict", aliases=["resource_tags"]
            ),
            vpc_id=dict(default=None, required=True),
            map_public=dict(default=False, required=False, type="bool"),
        )
    )

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

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

    if region:
        connection = boto3_conn(
            module,
            conn_type="client",
            resource="ec2",
            region=region,
            endpoint=ec2_url,
            **aws_connect_params,
        )
    else:
        module.fail_json(msg="region must be specified")

    vpc_id = module.params.get("vpc_id")
    tags = module.params.get("tags")
    cidr = module.params.get("cidr")
    az = module.params.get("az")
    state = module.params.get("state")
    map_public = module.params.get("map_public")

    try:
        if state == "present":
            result = ensure_subnet_present(
                connection,
                module,
                vpc_id,
                cidr,
                az,
                tags,
                map_public,
                check_mode=module.check_mode,
            )
        elif state == "absent":
            result = ensure_subnet_absent(
                connection, module, vpc_id, cidr, check_mode=module.check_mode
            )
    except botocore.exceptions.ClientError as e:
        module.fail_json(
            msg=e.message,
            exception=traceback.format_exc(),
            **camel_dict_to_snake_dict(e.response),
        )

    module.exit_json(**result)