Merge branch 'stable-2.13'

* stable-2.13:
  Add null protection

Change-Id: I2d3d22da7147b3b5c5da395d362c85e693d3dc98
diff --git a/src/main/java/com/googlesource/gerrit/plugins/avatars/external/ExternalUrlAvatarProvider.java b/src/main/java/com/googlesource/gerrit/plugins/avatars/external/ExternalUrlAvatarProvider.java
index ca5444f..056a1f2 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/avatars/external/ExternalUrlAvatarProvider.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/avatars/external/ExternalUrlAvatarProvider.java
@@ -114,7 +114,7 @@
    */
   private String replaceInUrl(String placeholder, String url,
       String replacement) {
-    if (!url.contains(placeholder)) {
+    if (url == null || !url.contains(placeholder)) {
       return url;
     }