gitaly-git2go: Return empty error when no changes

When the tree before and after the cherry-pick are the same, it means
there's nothing to commit. So in this case return an `EmptyError`
instead of building the commit.

1 files changed, 9 insertions, 0 deletions

diff --git a/internal/git2go/gob.go b/internal/git2go/gob.go
index 7c4ef0554..9f9ff97b4 100644
--- a/internal/git2go/gob.go
+++ b/internal/git2go/gob.go
@@ -31,6 +31,7 @@ var registeredTypes = map[interface{}]struct{}{
 	FileNotFoundError(""):    {},
 	InvalidArgumentError(""): {},
 	HasConflictsError{}:      {},
+	EmptyError{}:             {},
 	IndexError(""):           {},
 }
 
@@ -62,6 +63,14 @@ func (err HasConflictsError) Error() string {
 	return "could not apply due to conflicts"
 }
 
+// EmptyError indicates the command, for example cherry-pick, did result in no
+// changes, so the result is empty.
+type EmptyError struct{}
+
+func (err EmptyError) Error() string {
+	return "could not apply because the result was empty"
+}
+
 // SerializableError returns an error that is Gob serializable.
 // Registered types are serialized directly. Unregistered types
 // are transformed in to an opaque error using their error message.