Github reference is not a tree

Describes the cause and action for error messages.

Error Message(English)：
reference is not a tree

Resolution

Git submodule head 'reference is not a tree' error - Stack Overflow
https://stackoverflow.com/questions/2155887/git-submodule-head-reference-is-not-a-tree-error

composer package reference is not a tree
https://stackoverflow.com/questions/52976612/composer-package-reference-is-not-a-tree

pip: "Reference is not a tree" error when trying to install from ...
https://stackoverflow.com/questions/44726127/pip-reference-is-not-a-tree-error-when-trying-to-instal・・・

Git - Fatal: Reference is not a Tree - Local Submodule ...
https://stackoverflow.com/questions/36301758/git-fatal-reference-is-not-a-tree-local-submodule-direc・・・

git checkout throws fatal reference is not a tree
https://stackoverflow.com/questions/16363909/git-checkout-throws-fatal-reference-is-not-a-tree

Jenkins: git checkout fails with "reference is not a tree" error. - GitHub
https://github.com/grpc/grpc/issues/3428

git checkout fails with "reference is not a tree" ・ Issue #27462 ... - GitHub
https://github.com/kubernetes/kubernetes/issues/27462

gitで過去の特定のファイルを持ってくる - Qiita
https://qiita.com/kumagi/items/591d934acc387df82c3b

"fatal: reference is not a tree"の解決法 - Hello, world! - s21g
http://blog.s21g.com/articles/1743