From 08da9bb09f6046c7344f537fc4a819ed03d23f55 Mon Sep 17 00:00:00 2001
From: Máximo Cuadros <mcuadros@gmail.com>
Date: Wed, 13 May 2020 11:58:48 +0200
Subject: plumbing: object, Commit.Patch support to as nil

---
 plumbing/object/commit.go      |  9 ++++++---
 plumbing/object/commit_test.go | 11 ++++++++++-
 plumbing/object/tree_test.go   | 11 +++++++++++
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/plumbing/object/commit.go b/plumbing/object/commit.go
index b27f20b..113cb29 100644
--- a/plumbing/object/commit.go
+++ b/plumbing/object/commit.go
@@ -87,9 +87,12 @@ func (c *Commit) PatchContext(ctx context.Context, to *Commit) (*Patch, error) {
 		return nil, err
 	}
 
-	toTree, err := to.Tree()
-	if err != nil {
-		return nil, err
+	var toTree *Tree
+	if to != nil {
+		toTree, err = to.Tree()
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	return fromTree.PatchContext(ctx, toTree)
diff --git a/plumbing/object/commit_test.go b/plumbing/object/commit_test.go
index 28a7a81..e260a7f 100644
--- a/plumbing/object/commit_test.go
+++ b/plumbing/object/commit_test.go
@@ -12,8 +12,8 @@ import (
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/cache"
 
-	. "gopkg.in/check.v1"
 	"github.com/go-git/go-git/v5/storage/filesystem"
+	. "gopkg.in/check.v1"
 )
 
 type SuiteCommit struct {
@@ -188,6 +188,15 @@ Binary files /dev/null and b/binary.jpg differ
 	c.Assert(buf.String(), Equals, patch.String())
 }
 
+func (s *SuiteCommit) TestPatchContext_ToNil(c *C) {
+	from := s.commit(c, plumbing.NewHash("918c48b83bd081e863dbe1b80f8998f058cd8294"))
+
+	patch, err := from.PatchContext(context.Background(), nil)
+	c.Assert(err, IsNil)
+
+	c.Assert(len(patch.String()), Equals, 242679)
+}
+
 func (s *SuiteCommit) TestCommitEncodeDecodeIdempotent(c *C) {
 	ts, err := time.Parse(time.RFC3339, "2006-01-02T15:04:05-07:00")
 	c.Assert(err, IsNil)
diff --git a/plumbing/object/tree_test.go b/plumbing/object/tree_test.go
index 474bb6a..d9dad47 100644
--- a/plumbing/object/tree_test.go
+++ b/plumbing/object/tree_test.go
@@ -377,6 +377,17 @@ func (s *TreeSuite) TestTreeWalkerNextNonRecursive(c *C) {
 	c.Assert(count, Equals, 8)
 }
 
+func (s *TreeSuite) TestPatchContext_ToNil(c *C) {
+	commit := s.commit(c, plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5"))
+	tree, err := commit.Tree()
+	c.Assert(err, IsNil)
+
+	patch, err := tree.PatchContext(context.Background(), nil)
+	c.Assert(err, IsNil)
+
+	c.Assert(len(patch.String()), Equals, 242971)
+}
+
 func (s *TreeSuite) TestTreeWalkerNextSubmodule(c *C) {
 	dotgit := fixtures.ByURL("https://github.com/git-fixtures/submodule.git").One().DotGit()
 	st := filesystem.NewStorage(dotgit, cache.NewObjectLRUDefault())
-- 
cgit