Subversion command line - Killed 9 error message

I found searching through GitHub issues that some people had success reinstalling subversion and all of its dependencies like:

brew reinstall subversion $(brew deps subversion)

This actually resolved the issue for me, and fixed the same issue I saw with another homebrew package (which must have had a common dependency).

I didn't find an explanation as to why this resolves the issue. Either the signatures can become corrupt, or a newer version of homebrew makes a change to fix the problem. If you aren't running the latest homebrew it is probably a good idea to update first then reinstall.