From d0c0e2510b4467245092c95aad0ec4c3d3c2f8fa Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Sun, 7 May 2017 12:07:59 +0200
Subject: [PATCH] zfs: FilesystemDiff: support empty left list = no common
 ancestor

---
 zfs/diff.go | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/zfs/diff.go b/zfs/diff.go
index 90927a7..a10130c 100644
--- a/zfs/diff.go
+++ b/zfs/diff.go
@@ -138,6 +138,17 @@ func ZFSListFilesystemVersions(fs DatasetPath) (res []FilesystemVersion, err err
 // names are unique (bas ZFS_PROP_GUID replacement)
 func MakeFilesystemDiff(left, right []FilesystemVersion) (diff FilesystemDiff) {
 
+	if right == nil {
+		panic("right must not be nil")
+	}
+	if left == nil { // treat like no common ancestor
+		diff = FilesystemDiff{
+			IncrementalPath: nil,
+			Diverged:        false,
+			MRCAPathRight:   right,
+		}
+	}
+
 	// Assert both left and right are sorted by createtxg
 	var leftSorted, rightSorted fsbyCreateTXG
 	leftSorted = left