--ip-tags failure when used in "az network public-ip create" command

[magole]

Describe the bug
If --ip-tags is specified, the command fails with the error:

Unable to build a model: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get', DeserializationError: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get'
Traceback (most recent call last):
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1281, in _deserialize
    found_value = key_extractor(attr, attr_desc, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1072, in rest_key_case_insensitive_extractor
    return attribute_key_case_insensitive_extractor(key, None, working_data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1095, in attribute_key_case_insensitive_extractor
    return data.get(found_key)
AttributeError: 'str' object has no attribute 'get'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 565, in body
    data = deserializer._deserialize(data_type, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1251, in _deserialize
    self._deserialize(local_type, value)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1260, in _deserialize
    return self.deserialize_data(data, response)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1466, in deserialize_data
    return self.deserialize_type[iter_type](data, data_type[1:-1])
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1497, in deserialize_iter
    return [self.deserialize_data(a, iter_type) for a in attr]
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1497, in <listcomp>
    return [self.deserialize_data(a, iter_type) for a in attr]
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1479, in deserialize_data
    return self._deserialize(obj_type, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1291, in _deserialize
    raise_with_traceback(DeserializationError, msg, err)
  File "/opt/az/lib/python3.6/site-packages/msrest/exceptions.py", line 54, in raise_with_traceback
    raise error.with_traceback(exc_traceback)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1281, in _deserialize
    found_value = key_extractor(attr, attr_desc, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1072, in rest_key_case_insensitive_extractor
    return attribute_key_case_insensitive_extractor(key, None, working_data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1095, in attribute_key_case_insensitive_extractor
    return data.get(found_key)
msrest.exceptions.DeserializationError: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/az/lib/python3.6/site-packages/knack/cli.py", line 197, in invoke
    cmd_result = self.invocation.execute(args)
  File "/opt/az/lib/python3.6/site-packages/azure/cli/core/commands/__init__.py", line 369, in execute
    six.reraise(*sys.exc_info())
  File "/opt/az/lib/python3.6/site-packages/six.py", line 693, in reraise
    raise value
  File "/opt/az/lib/python3.6/site-packages/azure/cli/core/commands/__init__.py", line 343, in execute
    result = cmd(params)
  File "/opt/az/lib/python3.6/site-packages/azure/cli/core/commands/__init__.py", line 182, in __call__
    return self.handler(*args, **kwargs)
  File "/opt/az/lib/python3.6/site-packages/azure/cli/core/__init__.py", line 436, in default_command_handler
    result = op(**command_args)
  File "/opt/az/lib/python3.6/site-packages/azure/cli/command_modules/network/custom.py", line 2774, in create_public_ip
    return client.create_or_update(resource_group_name, public_ip_address_name, public_ip)
  File "/opt/az/lib/python3.6/site-packages/azure/mgmt/network/v2018_08_01/operations/public_ip_addresses_operations.py", line 274, in create_or_update
    **operation_config
  File "/opt/az/lib/python3.6/site-packages/azure/mgmt/network/v2018_08_01/operations/public_ip_addresses_operations.py", line 219, in _create_or_update_initial
    body_content = self._serialize.body(parameters, 'PublicIPAddress')
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 568, in body
    SerializationError, "Unable to build a model: "+str(err), err)
  File "/opt/az/lib/python3.6/site-packages/msrest/exceptions.py", line 54, in raise_with_traceback
    raise error.with_traceback(exc_traceback)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 565, in body
    data = deserializer._deserialize(data_type, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1251, in _deserialize
    self._deserialize(local_type, value)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1260, in _deserialize
    return self.deserialize_data(data, response)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1466, in deserialize_data
    return self.deserialize_type[iter_type](data, data_type[1:-1])
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1497, in deserialize_iter
    return [self.deserialize_data(a, iter_type) for a in attr]
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1497, in <listcomp>
    return [self.deserialize_data(a, iter_type) for a in attr]
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1479, in deserialize_data
    return self._deserialize(obj_type, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1291, in _deserialize
    raise_with_traceback(DeserializationError, msg, err)
  File "/opt/az/lib/python3.6/site-packages/msrest/exceptions.py", line 54, in raise_with_traceback
    raise error.with_traceback(exc_traceback)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1281, in _deserialize
    found_value = key_extractor(attr, attr_desc, data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1072, in rest_key_case_insensitive_extractor
    return attribute_key_case_insensitive_extractor(key, None, working_data)
  File "/opt/az/lib/python3.6/site-packages/msrest/serialization.py", line 1095, in attribute_key_case_insensitive_extractor
    return data.get(found_key)
msrest.exceptions.SerializationError: Unable to build a model: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get', DeserializationError: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get'

To Reproduce
az network public-ip create --name "MyIpName" --resource-group "MyResourceGroupName" --allocation-method Static --location EastUS2 --sku Basic --version IPv4 --zone 1 --ip-tags "MyIpTag=Blah"

Expected behavior
Valid description of failure or successfully executed command.

Environment summary
Azure Portal prompt

Additional context
If you skip the --ip-tags, the IP is successfully created.