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##### SUMMARY
<!--- Explain the problem briefly below -->
Nxos_l2_interfaces module fails with a traceback if allowed vlans are not preconfigured on interfaces, raised from PR fix #66517

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
nxos_l2_interfaces

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
2.9
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```

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

##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->
Try running the module for configuring allowed vlans for the 1st time.
<!--- Paste example playbooks or commands between quotes below -->
```yaml
    - nxos_l2_interfaces:
        config:
          - name: Ethernet2/2
            mode: trunk
            trunk:
              allowed_vlans: "10-12"
        state: merged
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
If allowed vlans are not preconfigured, the module should go ahead and configure the user-provided allowed vlans

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
If allowed vlans are not preconfigured, it fails with below traceback
<!--- Paste verbatim command output between quotes -->
```paste below
The full traceback is:
Traceback (most recent call last):
  File "/Users/sjaiswal/.ansible/tmp/ansible-local-34163u8gljr/ansible-tmp-1581928344.74-175330388156897/AnsiballZ_nxos_l2_interfaces.py", line 102, in <module>
    _ansiballz_main()
  File "/Users/sjaiswal/.ansible/tmp/ansible-local-34163u8gljr/ansible-tmp-1581928344.74-175330388156897/AnsiballZ_nxos_l2_interfaces.py", line 94, in _ansiballz_main
    invoke_module(zipped_mod, temp_path, ANSIBALLZ_PARAMS)
  File "/Users/sjaiswal/.ansible/tmp/ansible-local-34163u8gljr/ansible-tmp-1581928344.74-175330388156897/AnsiballZ_nxos_l2_interfaces.py", line 40, in invoke_module
    runpy.run_module(mod_name='ansible.modules.network.nxos.nxos_l2_interfaces', init_globals=None, run_name='__main__', alter_sys=True)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 188, in run_module
    fname, loader, pkg_name)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 82, in _run_module_code
    mod_name, mod_fname, mod_loader, pkg_name)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/modules/network/nxos/nxos_l2_interfaces.py", line 283, in <module>
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/modules/network/nxos/nxos_l2_interfaces.py", line 278, in main
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/module_utils/network/nxos/config/l2_interfaces/l2_interfaces.py", line 69, in execute_module
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/module_utils/network/nxos/config/l2_interfaces/l2_interfaces.py", line 103, in set_config
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/module_utils/network/nxos/config/l2_interfaces/l2_interfaces.py", line 136, in set_state
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/module_utils/network/nxos/config/l2_interfaces/l2_interfaces.py", line 205, in _state_merged
  File "/var/folders/n7/73s22vps0ls44ng__t8mwtl40000gn/T/ansible_nxos_l2_interfaces_payload_QGTQ63/ansible_nxos_l2_interfaces_payload.zip/ansible/module_utils/network/nxos/config/l2_interfaces/l2_interfaces.py", line 287, in set_commands
KeyError: 'allowed_vlans'
```

commands = []
        if not obj or len(obj.keys()) == 1:
            return commands
        cmd = 'no switchport '
        if 'vlan' in obj:
            commands.append(cmd + 'access vlan')
        if 'allowed_vlans' in obj:
            commands.append(cmd + 'trunk allowed vlan')
        if 'native_vlan' in obj:
            commands.append(cmd + 'trunk native vlan')
        if commands:
            commands.insert(0, 'interface ' + obj['name'])
        return commands
    def diff_of_dicts(self, w, obj):