From e0a5698af99da4f42f4af38df69889da490c938a Mon Sep 17 00:00:00 2001
From: Kevin Atkinson <k@kevina.org>
Date: Tue, 28 Aug 2018 22:30:41 -0400
Subject: [PATCH] Add IsNil() method.

---
 cid.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/cid.go b/cid.go
index 786dbf9..cf7fcc6 100644
--- a/cid.go
+++ b/cid.go
@@ -161,8 +161,17 @@ func NewCidV1(codecType uint64, mhash mh.Multihash) Cid {
 // - hash mh.Multihash
 type Cid struct{ str string }
 
+// Nil can be used to represent a nil Cid, using Cid{} directly is
+// also acceptable.
 var Nil = Cid{}
 
+// Nil returns true if a Cid is uninitialized or the Nil value.
+// Calling any other methods on an uninitialized Cid will result in
+// undefined behavior.
+func (c Cid) IsNil() bool {
+	return c.str == ""
+}
+
 // Parse is a short-hand function to perform Decode, Cast etc... on
 // a generic interface{} type.
 func Parse(v interface{}) (Cid, error) {