Getting this error when building Thunderbird. The line that it's having a problem with is:
thunderbird-packages.txt:comm/build/virtualenv_packages.txt

./mach create-mach-environment
Error running mach:

    ['create-mach-environment']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.
You can invoke |./mach busted| to check if this issue is already on file. If it
isn't, please use |./mach busted file create-mach-environment| to report it. If |./mach busted| is
misbehaving, you can also inspect the dependencies of bug 1543241.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

ValueError: not enough values to unpack (expected 2, got 1)

  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/mach_commands.py", line 2473, in create_mach_environment
    if manager.up_to_date() and not force:
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/virtualenv.py", line 176, in up_to_date
    env_requirements = self._requirements()
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/virtualenv.py", line 333, in _requirements
    return MachEnvRequirements.from_requirements_definition(
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 69, in from_requirements_definition
    _parse_mach_env_requirements(
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 129, in _parse_mach_env_requirements
    _parse_requirements_definition_file(root_requirements_path)
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 127, in _parse_requirements_definition_file
    _parse_requirements_line(line)
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 89, in _parse_requirements_line
    _parse_requirements_definition_file(nested_definition_path)
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 127, in _parse_requirements_definition_file
    _parse_requirements_line(line)
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 115, in _parse_requirements_line
    _parse_requirements_line(params, is_thunderbird_packages_txt=True)
  File "/home/rob/moz/unified2/python/mozbuild/mozbuild/requirements.py", line 83, in _parse_requirements_line
    action, params = line.rstrip().split(":", maxsplit=1)

https://hg.mozilla.org/mozilla-central/rev/4e8e2d84e5b1