1.0.0: 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 build/sphinx/man
Running Sphinx v6.1.3
WARNING: Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
making output directory... done
WARNING: html_static_path entry '_static' does not exist
building [mo]: targets for 0 po files that are out of date
writing output...
building [man]: all manpages
updating environment: [new config] 3 added, 0 changed, 0 removed
reading sources... [100%] index
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler.detect:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler.detect, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler.export:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler.export, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler.format:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler.format, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler.load:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler.load, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.BaseHandler.split:1: WARNING: duplicate object description of frontmatter.default_handlers.BaseHandler.split, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.YAMLHandler:1: WARNING: duplicate object description of frontmatter.default_handlers.YAMLHandler, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.JSONHandler:1: WARNING: duplicate object description of frontmatter.default_handlers.JSONHandler, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/frontmatter/default_handlers.py:docstring of frontmatter.default_handlers.TOMLHandler:1: WARNING: duplicate object description of frontmatter.default_handlers.TOMLHandler, other instance in api, use :noindex: for one of them
/home/tkloczko/rpmbuild/BUILD/python-frontmatter-1.0.0/docs/index.rst:9: WARNING: duplicate object description of frontmatter, other instance in api, use :noindex: for one of them
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
writing... python-python-frontmatter.3 { handlers api } done
build succeeded, 12 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