# Buggy code
def _config_node(self, conanfile, conanref, down_reqs, down_ref, down_options):
    """update settings and option in the current ConanFile, computing actual
    requirement values, cause they can be overriden by downstream requires
    param settings: dict of settings values => {"os": "windows"}
    """
    try:
        conanfile.requires.output = self._output
        if hasattr(conanfile, "config"):
            if not conanref:
                self._output.warn(
                    "config() has been deprecated. Use config_options and configure"
                )
            conanfile.config()
        conanfile.config_options()
        conanfile.options.propagate_upstream(
            down_options, down_ref, conanref, self._output
        )
        if hasattr(conanfile, "config"):
            conanfile.config()
        conanfile.configure()

        conanfile.settings.validate()  # All has to be ok!
        conanfile.options.validate()

        # Update requirements (overwrites), computing new upstream
        conanfile.requirements()
        new_options = conanfile.options.values
        new_down_reqs = conanfile.requires.update(
            down_reqs, self._output, conanref, down_ref
        )
    except ConanException as e:
        raise ConanException("%s: %s" % (conanref or "Conanfile", str(e)))
    except Exception as e:
        msg = format_conanfile_exception(
            str(conanref or "Conanfile"), "config, config_options or configure", e
        )
        raise ConanException(msg)
    return new_down_reqs, new_options


# Traceback (AttributeError)
Traceback (most recent call last):
File "<string>", line 10, in <module>
File "<string>", line 6, in run
File "conan\conans\client\command.py", line 931, in main
File "conan\conans\client\command.py", line 833, in run
File "conan\conans\client\command.py", line 441, in install
File "conan\conans\client\manager.py", line 276, in install
File "conan\conans\client\manager.py", line 176, in _get_graph
File "conan\conans\client\loader.py", line 181, in load_conan_txt
File "conan\conans\client\loader.py", line 193, in parse_conan_txt
File "conan\conans\model\requires.py", line 121, in add
AttributeError: 'NoneType' object has no attribute 'werror'
conan returned -1

# Fixed code
def _config_node(self, conanfile, conanref, down_reqs, down_ref, down_options):
    """update settings and option in the current ConanFile, computing actual
    requirement values, cause they can be overriden by downstream requires
    param settings: dict of settings values => {"os": "windows"}
    """
    try:
        if hasattr(conanfile, "config"):
            if not conanref:
                self._output.warn(
                    "config() has been deprecated. Use config_options and configure"
                )
            conanfile.config()
        conanfile.config_options()
        conanfile.options.propagate_upstream(
            down_options, down_ref, conanref, self._output
        )
        if hasattr(conanfile, "config"):
            conanfile.config()
        conanfile.configure()

        conanfile.settings.validate()  # All has to be ok!
        conanfile.options.validate()

        # Update requirements (overwrites), computing new upstream
        conanfile.requirements()
        new_options = conanfile.options.values
        new_down_reqs = conanfile.requires.update(
            down_reqs, self._output, conanref, down_ref
        )
    except ConanException as e:
        raise ConanException("%s: %s" % (conanref or "Conanfile", str(e)))
    except Exception as e:
        msg = format_conanfile_exception(
            str(conanref or "Conanfile"), "config, config_options or configure", e
        )
        raise ConanException(msg)
    return new_down_reqs, new_options