os: avoid panic when testing errors on Plan 9

R=golang-dev, bradfitz, akumar
CC=golang-dev
https://golang.org/cl/6017043

diff --git a/src/pkg/os/error_plan9.go b/src/pkg/os/error_plan9.go
index 3c9dfb0b158b6381d73a8c7ea63303aebd9ca47e..f083a2d1de38dd35d3a940f20c6d5c6a8805b3c0 100644 (file)
--- a/src/pkg/os/error_plan9.go
+++ b/src/pkg/os/error_plan9.go
@@ -5,6 +5,9 @@
 package os
 
 func isExist(err error) bool {
+       if err == nil {
+               return false
+       }
        if pe, ok := err.(*PathError); ok {
                err = pe.Err
        }
@@ -12,6 +15,9 @@ func isExist(err error) bool {
 }
 
 func isNotExist(err error) bool {
+       if err == nil {
+               return false
+       }
        if pe, ok := err.(*PathError); ok {
                err = pe.Err
        }
@@ -19,6 +25,9 @@ func isNotExist(err error) bool {
 }
 
 func isPermission(err error) bool {
+       if err == nil {
+               return false
+       }
        if pe, ok := err.(*PathError); ok {
                err = pe.Err
        }