I found a bug of REST API.
I tried this way: https://confluence.atlassian.com/display/BITBUCKET/repository+Resource
"name" "The name for the repository. When omitted, this assumes that value of the repo_slug part of the URL (optional)."
But I haven't specified "name", it was managed as "" (zero bytes string as repository name). and some dashboard's history was broken. many 500 errors were happen.