Rails default Dockerfile build failed after added bootstrap gem

1. Create new project with importmap by default

rails new test_app
cd ../test_app
./bin/bundle add dartsass-rails
./bin/rails dartsass:install

2. Check if build is ok
   docker build .

Now let's produce error:

1. add bootstrap gem
   ./bin/bundle add bootstrap --git 'https://github.com/twbs/bootstrap-rubygem'
2. build it
   docker build .

throw error:

 => ERROR [8/8] RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile                                                                 1.3s
------                                                                                                                                         
 > [8/8] RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile:                                                                            
1.256 bin/rails aborted!                                                                                                                       
1.256 ExecJS::RuntimeUnavailable: Could not find a JavaScript runtime. See https://github.com/rails/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)

Installing node/etc is not the right solution because the main reason to use importmap is to drop the nodejs dependency. Any ideas on how to solve this?

Start by reproducing the issue with the listed rails new, dartsass:install, bootstrap gem, and docker build commands. Read the default Dockerfile and the assets:precompile failure, then determine why Bootstrap's build requires a JavaScript runtime under importmap. Done means the Docker build and asset precompile succeed without adding Node.js.