fix(dropdown): prevent null reference errors on dynamic positioning

Add a guard clause in the positionElement function to check for null
before accessing wrapperRef.current properties. This prevents runtime
errors related to attempting to access properties on null when the
dropdown component mounts or updates under certain conditions. Solves
Sentry errors "Cannot read properties of null (reading lastElementChild)"
and "null is not an object (evaluating r.lastElementChild)".

packages/sage-system/lib/dropdown.js

@@ -190,8 +190,12 @@ Sage.dropdown = (function () {
   }
 
   function positionElement(el) {
+    // Guard clause to check if wrapperRef.current is null
+    if (!wrapperRef.current) return;
+
     let directionX = null;
     let directionY = null;
+    const el = wrapperRef.current;
 
     // Elements
     const button = el;