The method getReferenceCommit() on a Repository works with a tag given in the form refs/tags/v0.1.5 only when the tag is a lightweight tag. If it is an annotated tag, calling this method results in an error:

Error: the requested type does not match the type in the ODB

See also the discussion at https://gitter.im/nodegit/nodegit?at=59b5026e66c1c7c477342023