Recover from nil pointers when logging

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

klog.go

@@ -847,7 +847,7 @@ func kvListFormat(b *bytes.Buffer, keysAndValues ...interface{}) {
 		// (https://github.com/kubernetes/kubernetes/pull/106594#issuecomment-975526235).
 		switch v := v.(type) {
 		case fmt.Stringer:
-			writeStringValue(b, true, v.String())
+			writeStringValue(b, true, StringertoString(v))
 		case string:
 			writeStringValue(b, true, v)
 		case error:
@@ -872,6 +872,16 @@ func kvListFormat(b *bytes.Buffer, keysAndValues ...interface{}) {
 	}
 }
 
+func StringertoString(s fmt.Stringer) (ret string) {
+	defer func() {
+		if err := recover(); err != nil {
+			ret = "nil"
+		}
+	}()
+	ret = s.String()
+	return ret
+}
+
 func writeStringValue(b *bytes.Buffer, quote bool, v string) {
 	data := []byte(v)
 	index := bytes.IndexByte(data, '\n')