Oid: make sure not to dereference a NULL git_oid

Some calls like Reference.Target() can return NULL if the reference is
symbolic. Make sure newOidFromC() can handle these situations.

1 files changed, 4 insertions, 0 deletions

diff --git a/git.go b/git.go
index 84716e3..68712d4 100644
--- a/git.go
+++ b/git.go
@@ -26,6 +26,10 @@ type Oid struct {
 }
 
 func newOidFromC(coid *C.git_oid) *Oid {
+	if coid == nil {
+		return nil
+	}
+
 	oid := new(Oid)
 	copy(oid.bytes[0:20], C.GoBytes(unsafe.Pointer(coid), 20))
 	return oid