Consider the following spec:

===============================
Name:           minversion-none
Version:        0
Release:        0
Summary:        ...
License:        MIT
BuildArch:      noarch

BuildRequires:  python3-devel

%description
...


%prep
touch setup.py
cat > tox.ini << EOF
[tox]
requires =
    you-cant-have-this
EOF


%generate_buildrequires
%pyproject_buildrequires -t
===============================

Build it with pyproject-rpm-macros 1.9.0-2.fc39.

You'll get:

+ /usr/bin/python3 -Bs /usr/lib/rpm/redhat/pyproject_buildrequires.py --generate-extras --python3_pkgversion 3 --wheeldir /builddir/build/BUILD/pyproject-wheeldir --output /builddir/build/BUILD/minversion-none-0-0.x86_64-pyproject-buildrequires -t
Handling setuptools >= 40.8 from default build backend
Requirement satisfied: setuptools >= 40.8
   (installed: setuptools 67.7.2)
Handling wheel from default build backend
Requirement satisfied: wheel
   (installed: wheel 0.40.0)
Handling wheel from get_requires_for_build_wheel
Requirement satisfied: wheel
   (installed: wheel 0.40.0)
Handling tox-current-env >= 0.0.6 from tox itself
Requirement satisfied: tox-current-env >= 0.0.6
   (installed: tox-current-env 0.0.11)
ROOT: HandledError| provisioning explicitly disabled within /usr/bin/python3, but is missing [requires (has)]: you-cant-have-this and wrote to /builddir/build/BUILD/.pyproject-builddir/tmpovnqr8qa
Handling tox >= None from tox provision (minversion)
Traceback (most recent call last):
  File "/usr/lib/python3.12/site-packages/packaging/requirements.py", line 35, in __init__
    parsed = _parse_requirement(requirement_string)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/packaging/_parser.py", line 64, in parse_requirement
    return _parse_requirement(Tokenizer(source, rules=DEFAULT_RULES))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/packaging/_parser.py", line 82, in _parse_requirement
    url, specifier, marker = _parse_requirement_details(tokenizer)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/packaging/_parser.py", line 126, in _parse_requirement_details
    marker = _parse_requirement_marker(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/packaging/_parser.py", line 147, in _parse_requirement_marker
    tokenizer.raise_syntax_error(
  File "/usr/lib/python3.12/site-packages/packaging/_tokenizer.py", line 165, in raise_syntax_error
    raise ParserSyntaxError(
packaging._tokenizer.ParserSyntaxError: Expected end or semicolon (after name and no valid version specifier)
    tox >= None
        ^

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 107, in add
    requirement = Requirement(requirement_str)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/packaging/requirements.py", line 37, in __init__
    raise InvalidRequirement(str(e)) from e
packaging.requirements.InvalidRequirement: Expected end or semicolon (after name and no valid version specifier)
    tox >= None
        ^

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 555, in main
    generate_requires(
  File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 454, in generate_requires
    generate_tox_requirements(toxenv, requirements)
  File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 390, in generate_tox_requirements
    requirements.add(f'tox >= {provision_requires["minversion"]}',
  File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 113, in add
    raise ValueError(message)
ValueError: Requirement 'tox >= None' from tox provision (minversion) is invalid.

RPM build warnings:

RPM build errors:
error: Bad exit status from /var/tmp/rpm-tmp.rR8yiJ (%generate_buildrequires)




This is caused by tox 4 incompatibility in pyproject_buildrequires.py

We have:

            provision_requires = json.loads(provision_content)
            if 'minversion' in provision_requires:
                requirements.add(f'tox >= {provision_requires["minversion"]}',
                                 source='tox provision (minversion)')

But tox 4 generates:

    {
        "minversion": null,
        "requires": [
            "you-cant-have-this",
            "tox"
        ]
    }

Hence we should update the conditional to check for non-None value.

Reproducible: Always

Steps to Reproduce:
1. Build the provided spec
Actual Results:  
Build fails with invalid Python requirements: Requirement 'tox >= None' from tox provision (minversion) is invalid.

Expected Results:  
Build fails with unmet RPM requirements: python3dist(you-cant-have-this)