Affects Version/s: None
Fix Version/s: None
(I'm filing this from memory, with no reproduction recipe at hand. Details could be wrong. Could even have been fixed, but I'm not aware it has.)
svn diff can print diff headers without diffs, when an external diff-cmd is configured, in certain cases:
It never shows this kind of output when using the internal diff.
What happens, roughly, is that if the low level diffing algorithm spits out anything through its "text changed" API, then the high level first prints this "Index:" header and then calls the configured external diff tool. In some cases the "text changed" API call can spit out a no-op, and in other cases it can spit out a real text change that consists only of changes that the external diff tool ignores, such as EOL-style changes. In either of those cases, you can get this result.
When this happens, it's often for a whole lot of files, e.g. all the files on a branch-creation diff, which makes it annoying.
(Need a reproduction recipe or test case.)