I have tried following command:

az resource tag --ids /subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rg1 --tags xxx=yyy

It crashed with following stacktrace:

The command failed with an unexpected error. Here is the traceback:

'namespace'
Traceback (most recent call last):
File "/env/lib/python3.6/site-packages/knack/cli.py", line 206, in invoke
cmd_result = self.invocation.execute(args)
File "/azure-cli/src/azure-cli-core/azure/cli/core/commands/init.py", line 578, in execute
raise ex
File "/azure-cli/src/azure-cli-core/azure/cli/core/commands/init.py", line 636, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/azure-cli/src/azure-cli-core/azure/cli/core/commands/init.py", line 629, in _run_job
six.reraise(*sys.exc_info())
File "/env/lib/python3.6/site-packages/six.py", line 693, in reraise
raise value
File "/azure-cli/src/azure-cli-core/azure/cli/core/commands/init.py", line 606, in _run_job
result = cmd_copy(params)
File "/azure-cli/src/azure-cli-core/azure/cli/core/commands/init.py", line 305, in call
return self.handler(*args, **kwargs)
File "/azure-cli/src/azure-cli-core/azure/cli/core/init.py", line 485, in default_command_handler
return op(**command_args)
File "/azure-cli/src/azure-cli/azure/cli/command_modules/resource/custom.py", line 928, in tag_resource
[_get_rsrc_util_from_parsed_id(cmd.cli_ctx, id_dict, api_version).tag(tags) for id_dict in parsed_ids])
File "/azure-cli/src/azure-cli/azure/cli/command_modules/resource/custom.py", line 928, in
[_get_rsrc_util_from_parsed_id(cmd.cli_ctx, id_dict, api_version).tag(tags) for id_dict in parsed_ids])
File "/azure-cli/src/azure-cli/azure/cli/command_modules/resource/custom.py", line 802, in _get_rsrc_util_from_parsed_id
api_version)
File "/azure-cli/src/azure-cli/azure/cli/command_modules/resource/custom.py", line 1802, in init
api_version = _ResourceUtils._resolve_api_version_by_id(self.rcf, resource_id)
File "/azure-cli/src/azure-cli/azure/cli/command_modules/resource/custom.py", line 2005, in _resolve_api_version_by_id
namespace = parts.get('child_namespace_1', parts['namespace'])
KeyError: 'namespace'