##### 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'

```

returned: always
  type: dict
  sample:
    arn: "arn:aws:lightsail:us-east-1:448830907657:Instance/1fef0175-d6c8-480e-84fa-214f969cda87"
    blueprint_id: "ubuntu_16_04"
    blueprint_name: "Ubuntu"
    bundle_id: "nano_1_0"
    created_at: "2017-03-27T08:38:59.714000-04:00"
    hardware:
      cpu_count: 1
      ram_size_in_gb: 0.5
    is_static_ip: false
    location:
      availability_zone: "us-east-1a"
      region_name: "us-east-1"
    name: "my_instance"
    networking:
      monthly_transfer:
        gb_per_month_allocated: 1024
      ports:
        - access_direction: "inbound"
          access_from: "Anywhere (0.0.0.0/0)"
          access_type: "public"
          common_name: ""
          from_port: 80
          protocol: tcp
          to_port: 80
        - access_direction: "inbound"
          access_from: "Anywhere (0.0.0.0/0)"
          access_type: "public"