Merge pull request #174 from jenkinsci/fix-173

use ionicons-api as default plugin for links as well

src/main/java/io/jenkins/plugins/customizable_header/AppNavLink.java

@@ -142,7 +142,7 @@ private static String extractPluginNameFromIconSrc(String iconSrc) {
     }
 
     if (!iconSrc.contains("plugin-")) {
-      return "";
+      return "ionicons-api";
     }
 
     String[] arr = iconSrc.split(" ");