Subclasses should override this to specify custom error types.

Subclasses should override this to specify custom param types.

Subclasses should override these methods with the proper result for the pertinent version control system, e.g. getGitResult for Git.

If the result is not supported for that VCS, do not implement it. e.g. Subversion (SVN) does not support branches.

This method is final because most queries will need to construct a DiffusionRequest and use it. Consolidating this codepath and enforcing getDiffusionRequest() works when we need it is good.

getResult() should be overridden by subclasses as necessary, e.g. there is a common operation across all version control systems that should occur after getResult(), like formatting a timestamp.