0.8.0: sphinx warnings reference target not found

[kloczek]

On building my packages I'm using sphinx-build command with -n switch which shows warmings about missing references. These are not critical issues.
Here is the output with warnings:

+ /usr/bin/sphinx-build -n -T -b man docs/source build/sphinx/man
Running Sphinx v6.2.1
WARNING: Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
making output directory... done
building [mo]: targets for 0 po files that are out of date
writing output...
building [man]: all manpages
updating environment: [new config] 10 added, 0 changed, 0 removed
reading sources... [100%] who
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
writing... python-sphinx-press-theme.3 { about configuration who changes theme-demo/index theme-demo/basic theme-demo/admonition theme-demo/domain theme-demo/extensions } /home/tkloczko/rpmbuild/BUILD/sphinx_press_theme-0.8.0/sphinx_press_theme/__init__.py:docstring of sphinx_press_theme.add_toctree_data:1: WARNING: py:class reference target not found: docutils.nodes.document
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector:3: WARNING: py:class reference target not found: sphinx.environment.BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.clear_doc:1: WARNING: py:class reference target not found: Sphinx
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.clear_doc:1: WARNING: py:class reference target not found: BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.get_outdated_docs:1: WARNING: py:class reference target not found: Sphinx
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.get_outdated_docs:1: WARNING: py:class reference target not found: BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.get_updated_docs:1: WARNING: py:class reference target not found: Sphinx
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.get_updated_docs:1: WARNING: py:class reference target not found: BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.merge_other:1: WARNING: py:class reference target not found: Sphinx
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.merge_other:1: WARNING: py:class reference target not found: BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.merge_other:1: WARNING: py:class reference target not found: BuildEnvironment
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.process_doc:1: WARNING: py:class reference target not found: Sphinx
/usr/lib/python3.8/site-packages/sphinx/environment/collectors/__init__.py:docstring of sphinx.environment.collectors.EnvironmentCollector.process_doc:1: WARNING: py:class reference target not found: nodes.document
/home/tkloczko/rpmbuild/BUILD/sphinx_press_theme-0.8.0/docs/source/theme-demo/basic.rst:: WARNING: "table cell spanning" not supported
done
build succeeded, 15 warnings.

You can peak on fixes that kind of issues in other projects
RDFLib/rdflib-sqlalchemy#95
RDFLib/rdflib#2036
click-contrib/sphinx-click@abc31069
frostming/unearth#14
jaraco/cssutils#21
latchset/jwcrypto#289
latchset/jwcrypto#289
pypa/distlib@98b9b89f
pywbem/pywbem#2895
sissaschool/elementpath@bf869d9e
sissaschool/xmlschema@42ea98f2
sqlalchemy/sqlalchemy@5e88e6e8