# Buggy code
def main():
    """main entry point for module execution"""
    element_spec = dict(
        name=dict(),
        mode=dict(choices=["access", "trunk"]),
        access_vlan=dict(),
        native_vlan=dict(type="int"),
        trunk_vlans=dict(type="list"),
        unit=dict(default=0, type="int"),
        description=dict(),
        state=dict(default="present", choices=["present", "absent"]),
        active=dict(default=True, type="bool"),
    )

    aggregate_spec = deepcopy(element_spec)
    aggregate_spec["name"] = dict(required=True)

    # remove default in aggregate spec, to handle common arguments
    remove_default_spec(aggregate_spec)

    required_one_of = [["name", "aggregate"]]
    mutually_exclusive = [
        ["name", "aggregate"],
        ["access_vlan", "trunk_vlans"],
        ["access_vlan", "native_vlan"],
    ]

    required_if = [
        ("mode", "access", ("access_vlan",)),
        ("mode", "trunk", ("trunk_vlans",)),
    ]

    argument_spec = dict(
        aggregate=dict(
            type="list",
            elements="dict",
            options=aggregate_spec,
            mutually_exclusive=mutually_exclusive,
            required_if=required_if,
        ),
    )

    argument_spec.update(element_spec)
    argument_spec.update(junos_argument_spec)

    module = AnsibleModule(
        argument_spec=argument_spec,
        supports_check_mode=True,
        mutually_exclusive=mutually_exclusive,
        required_one_of=required_one_of,
        required_if=required_if,
    )

    warnings = list()
    result = {"changed": False}

    if warnings:
        result["warnings"] = warnings

    top = "interfaces/interface"

    param_to_xpath_map = collections.OrderedDict()
    param_to_xpath_map.update(
        [
            ("name", {"xpath": "name", "is_key": True}),
            ("unit", {"xpath": "name", "top": "unit", "is_key": True}),
            (
                "mode",
                {"xpath": "interface-mode", "top": "unit/family/ethernet-switching"},
            ),
            (
                "access_vlan",
                {"xpath": "members", "top": "unit/family/ethernet-switching/vlan"},
            ),
            (
                "trunk_vlans",
                {"xpath": "members", "top": "unit/family/ethernet-switching/vlan"},
            ),
            ("native_vlan", {"xpath": "native-vlan-id"}),
            ("description", "description"),
        ]
    )

    params = to_param_list(module)

    requests = list()
    for param in params:
        # if key doesn't exist in the item, get it from module.params
        for key in param:
            if param.get(key) is None:
                param[key] = module.params[key]

        item = param.copy()

        validate_param_values(module, param_to_xpath_map, param=item)

        want = map_params_to_obj(module, param_to_xpath_map, param=item)
        requests.append(map_obj_to_ele(module, want, top, param=item))

    diff = None
    with locked_config(module):
        for req in requests:
            diff = load_config(module, tostring(req), warnings, action="replace")

        commit = not module.check_mode
        if diff:
            if commit:
                commit_configuration(module)
            else:
                discard_changes(module)
            result["changed"] = True

            if module._diff:
                result["diff"] = {"prepared": diff}

    module.exit_json(**result)


# Traceback (ansible.module_utils.connection.ConnectionError)
The full traceback is:
Traceback (most recent call last):
File "/tmp/ansible_9oFhCt/ansible_module_junos_l2_interface.py", line 266, in <module>
main()
File "/tmp/ansible_9oFhCt/ansible_module_junos_l2_interface.py", line 249, in main
diff = load_config(module, tostring(req), warnings, action='replace')
File "/tmp/ansible_9oFhCt/ansible_modlib.zip/ansible/module_utils/network/junos/junos.py", line 211, in load_config
File "/tmp/ansible_9oFhCt/ansible_modlib.zip/ansible/module_utils/network/common/netconf.py", line 76, in __rpc__
File "/tmp/ansible_9oFhCt/ansible_modlib.zip/ansible/module_utils/network/common/netconf.py", line 108, in parse_rpc_error
ansible.module_utils.connection.ConnectionError: error: Access interface <ge-0/0/34.0> has more than one vlan member: <v20> and <v10>
error: configuration check-out failed

# Fixed code
def main():
    """main entry point for module execution"""
    element_spec = dict(
        name=dict(),
        mode=dict(choices=["access", "trunk"]),
        access_vlan=dict(),
        native_vlan=dict(type="int"),
        trunk_vlans=dict(type="list"),
        unit=dict(default=0, type="int"),
        description=dict(),
        enhanced_layer=dict(default=True, type="bool"),
        state=dict(default="present", choices=["present", "absent"]),
        active=dict(default=True, type="bool"),
    )

    aggregate_spec = deepcopy(element_spec)
    aggregate_spec["name"] = dict(required=True)

    # remove default in aggregate spec, to handle common arguments
    remove_default_spec(aggregate_spec)

    required_one_of = [["name", "aggregate"]]
    mutually_exclusive = [
        ["name", "aggregate"],
        ["access_vlan", "trunk_vlans"],
        ["access_vlan", "native_vlan"],
    ]

    required_if = [
        ("mode", "access", ("access_vlan",)),
        ("mode", "trunk", ("trunk_vlans",)),
    ]

    argument_spec = dict(
        aggregate=dict(
            type="list",
            elements="dict",
            options=aggregate_spec,
            mutually_exclusive=mutually_exclusive,
            required_if=required_if,
        ),
    )

    argument_spec.update(element_spec)
    argument_spec.update(junos_argument_spec)

    module = AnsibleModule(
        argument_spec=argument_spec,
        supports_check_mode=True,
        mutually_exclusive=mutually_exclusive,
        required_one_of=required_one_of,
        required_if=required_if,
    )

    warnings = list()
    result = {"changed": False}

    if warnings:
        result["warnings"] = warnings

    top = "interfaces/interface"

    param_to_xpath_map = collections.OrderedDict()
    param_to_xpath_map.update(
        [
            ("name", {"xpath": "name", "is_key": True}),
            ("unit", {"xpath": "name", "top": "unit", "is_key": True}),
            (
                "mode",
                {"xpath": "interface-mode", "top": "unit/family/ethernet-switching"},
            ),
            (
                "access_vlan",
                {"xpath": "members", "top": "unit/family/ethernet-switching/vlan"},
            ),
            (
                "trunk_vlans",
                {"xpath": "members", "top": "unit/family/ethernet-switching/vlan"},
            ),
            ("native_vlan", {"xpath": "native-vlan-id"}),
            ("description", "description"),
        ]
    )

    params = to_param_list(module)

    requests = list()
    for param in params:
        # if key doesn't exist in the item, get it from module.params
        for key in param:
            if param.get(key) is None:
                param[key] = module.params[key]

        item = param.copy()

        validate_param_values(module, param_to_xpath_map, param=item)

        param_to_xpath_map["mode"]["xpath"] = (
            "interface-mode" if param["enhanced_layer"] else "port-mode"
        )

        want = map_params_to_obj(module, param_to_xpath_map, param=item)
        requests.append(map_obj_to_ele(module, want, top, param=item))

    diff = None
    with locked_config(module):
        for req in requests:
            diff = load_config(module, tostring(req), warnings, action="replace")

        commit = not module.check_mode
        if diff:
            if commit:
                commit_configuration(module)
            else:
                discard_changes(module)
            result["changed"] = True

            if module._diff:
                result["diff"] = {"prepared": diff}

    module.exit_json(**result)