##### SUMMARY
The delete operation of the `lightsail` module is not idempotent. If the instance is already deleted, then the task generates a traceback.

```
Traceback (most recent call last):
  File "ansible/modules/cloud/amazon/lightsail.py", line 458, in main
  File "ansible/modules/cloud/amazon/lightsail.py", line 422, in core
  File "ansible/module_utils/common/dict_transformations.py", line 42, in camel_dict_to_snake_dict
    for k, v in camel_dict.items():
AttributeError: 'NoneType' object has no attribute 'items'
```

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
`lightsail`

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.10.0.dev0
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
nothing
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->
Python 3.7.4

##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- lightsail:
    state: absent
    name: my_instance
```

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
Task successfully returns with `changed: false`.

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
Instead this traceback is generated - 
<!--- Paste verbatim command output between quotes -->
```paste below
Traceback (most recent call last):
  File "ansible/modules/cloud/amazon/lightsail.py", line 458, in main
  File "ansible/modules/cloud/amazon/lightsail.py", line 422, in core
  File "ansible/module_utils/common/dict_transformations.py", line 42, in camel_dict_to_snake_dict
    for k, v in camel_dict.items():
AttributeError: 'NoneType' object has no attribute 'items'

```

argument_spec = ec2_argument_spec()
    argument_spec.update(dict(
        name=dict(type='str', required=True),
        state=dict(type='str', default='present', choices=['present', 'absent', 'stopped', 'running', 'restarted']),
        zone=dict(type='str'),
        blueprint_id=dict(type='str'),
        bundle_id=dict(type='str'),
        key_pair_name=dict(type='str'),
        user_data=dict(type='str'),
        wait=dict(type='bool', default=True),
        wait_timeout=dict(default=300, type='int'),
    ))
    module = AnsibleModule(argument_spec=argument_spec)
    if not HAS_BOTO3:
        module.fail_json(msg='Python module "boto3" is missing, please install it')
    if not HAS_BOTOCORE:
        module.fail_json(msg='Python module "botocore" is missing, please install it')
    try:
        core(module)
    except (botocore.exceptions.ClientError, Exception) as e:
        module.fail_json(msg=str(e), exception=traceback.format_exc())
if __name__ == '__main__':
    main()