When examining the contents of git commits, running "Log Selected..." on files with names that begin with a period results in a dialog box with the following error:

Potential security issue detected in the specified URL.

Sourcetree determined this URL is in an unsupported format.

To reproduce, select a git commit that contains a file with a name beginning with a period (e.g. ".gitignore"), right-click on that file and select "Log Selected...".

Spotted in SourceTree for Mac 2.7 (152), but this may affect other versions.