git source from documentation does not work

https://docs.conan.io/en/latest/developing_packages/package_dev_flow.html

how to reproduce:

cd ... /conan-center-index/recipes/zlib/all
execute command from docs:
conan source . --source-folder=tmp/source

got an error:
conanfile.py (zlib/None): Configuring sources in /home/andrei/sources/conan-center-index/recipes/zlib/all/tmp/source
conanfile.py (zlib/None): Executing exports to: /home/andrei/sources/conan-center-index/recipes/zlib/all/tmp/source
conanfile.py (zlib/None) exports: File 'conandata.yml' found. Exporting it...
conanfile.py (zlib/None) exports: Copied 1 '.yml' file: conandata.yml
conanfile.py (zlib/None): Calling export_sources()
conanfile.py (zlib/None) export_sources() method: Copied 1 '.txt' file: CMakeLists.txt
ERROR: conanfile.py (zlib/None): Error in source() method, line 57
tools.get(**self.conan_data["sources"][self.version],
KeyError: None