diff --git a/src/core.js b/src/core.js
index 584ead6..c36b848 100644
--- a/src/core.js
+++ b/src/core.js
@@ -65,6 +65,10 @@ const Bulma = {
         var classes = [];
 
         for(var key in this.plugins) {
+            if(!this.plugins[key].getRootClass()) {
+                continue;
+            }
+
             classes.push('.' + this.plugins[key].getRootClass());
         }