Error #2 when trying to install ECM (Extra Cmake Modules)

I am trying to install extra-cmake-modules from source, and then I get an error after executing make command:

Extension error:
Could not import extension ecm (exception: No module named 'sphinxcontrib')
make[2]: *** [docs/CMakeFiles/documentation.dir/build.make:62: docs/doc_format_html] Error 2
make[2]: Leaving directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make[1]: *** [CMakeFiles/Makefile2:217: docs/CMakeFiles/documentation.dir/all] Error 2
make[1]: Leaving directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make: *** [Makefile:163: all] Error 2

It seems that the problem is about module Sphinx, but I tried to uninstall and install it again via pip and the error still occurred. So what can I do to fix it?
Here are logs when I executed cmake -DCMAKE_INSTALL_PREFIX=/usr .. and make command:

$ cmake -DCMAKE_INSTALL_PREFIX=/usr ..
-- WARNING: skipping tests that require PyQt
-- The following features have been enabled:

 * BUILD_HTML_DOCS, Generate HTML documentation for installed modules.
 * BUILD_MAN_DOCS, Generate man page documentation for installed modules.
 * BUILD_TESTING, Build automated tests.

-- The following OPTIONAL packages have been found:

 * Sphinx (required version >= 1.2), Tool to generate documentation., <https://www.sphinx-doc.org/>
   Required to build documentation for Extra CMake Modules.
 * QCollectionGenerator, Qt help collection generator., <https://www.qt.io/>
   Required to build Extra CMake Modules documentation in Qt Help format.
 * Qt5LinguistTools, Qt5 linguist tools., <https://www.qt.io/>
   Required to run tests for the ECMPoQmTools module.
 * Qt5Core, Qt5 core library., <https://www.qt.io/>
   Required to run tests for the ECMQtDeclareLoggingCategory module, and for some tests of the KDEInstallDirs module.
 * Qt5Network (required version >= 5.14.2)
 * Qt5Qml (required version >= 5.14.2)
 * Qt5QmlModels (required version >= 5.14.2)
 * Qt5Gui (required version >= 5.14.2)
 * Qt5Quick, Qt5 Quick library., <https://www.qt.io/>
   Required to run tests for the ECMQMLModules module.

-- The following features have been disabled:

 * BUILD_QTHELP_DOCS, Generate QtHelp documentation for installed modules.

-- Configuring done
-- Generating done
-- Build files have been written to: /home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build
$ make
make[1]: Entering directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make[2]: Entering directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make[2]: Leaving directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make[2]: Entering directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
[ 50%] sphinx-build html: see /home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build/docs/build-html.log
/usr/lib/python3.8/importlib/__init__.py:127: RemovedInSphinx40Warning: The alias 'sphinx.util.pycompat.htmlescape' is deprecated, use 'html.escape' instead. Check CHANGES for Sphinx API modifications.
  return _bootstrap._gcd_import(name[level:], package, level)

Extension error:
Could not import extension ecm (exception: No module named 'sphinxcontrib')
make[2]: *** [docs/CMakeFiles/documentation.dir/build.make:62: docs/doc_format_html] Error 2
make[2]: Leaving directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make[1]: *** [CMakeFiles/Makefile2:217: docs/CMakeFiles/documentation.dir/all] Error 2
make[1]: Leaving directory '/home/masterpi/Documents/Extra-CMake-Modules/extra-cmake-modules/build'
make: *** [Makefile:163: all] Error 2

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Author: Minh Nhật