From 7b2c5ac9fc04fc5efafb60700713d4fa609b777b Mon Sep 17 00:00:00 2001
From: Thomas Cyron <thomas@thcyron.de>
Date: Thu, 12 Oct 2017 20:25:33 +0200
Subject: [PATCH] Create new buffer if not present yet (#549)

Fixes a nil dereference when TraverseChildren is used
with multiple subcommands.
---
 command.go      |  3 +++
 command_test.go | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/command.go b/command.go
index 4d4b391ec..58e6ceb07 100644
--- a/command.go
+++ b/command.go
@@ -1360,6 +1360,9 @@ func (c *Command) ParseFlags(args []string) error {
 		return nil
 	}
 
+	if c.flagErrorBuf == nil {
+		c.flagErrorBuf = new(bytes.Buffer)
+	}
 	beforeErrorBufLen := c.flagErrorBuf.Len()
 	c.mergePersistentFlags()
 	err := c.Flags().Parse(args)
diff --git a/command_test.go b/command_test.go
index 4f798da2f..dda355f36 100644
--- a/command_test.go
+++ b/command_test.go
@@ -439,6 +439,32 @@ func TestTraverseWithBadChildFlag(t *testing.T) {
 	}
 }
 
+func TestTraverseWithTwoSubcommands(t *testing.T) {
+	cmd := &Command{
+		Use:              "do",
+		TraverseChildren: true,
+	}
+
+	sub := &Command{
+		Use:              "sub",
+		TraverseChildren: true,
+	}
+	cmd.AddCommand(sub)
+
+	subsub := &Command{
+		Use: "subsub",
+	}
+	sub.AddCommand(subsub)
+
+	c, _, err := cmd.Traverse([]string{"sub", "subsub"})
+	if err != nil {
+		t.Fatalf("Expected no error: %s", err)
+	}
+	if c.Name() != subsub.Name() {
+		t.Fatalf("wrong command %q expected %q", c.Name(), subsub.Name())
+	}
+}
+
 func TestRequiredFlags(t *testing.T) {
 	c := &Command{Use: "c", Run: func(*Command, []string) {}}
 	output := new(bytes.Buffer)