fix: whiteboard page sidebar empty string (#10018)

src/main/frontend/util/property.cljs

@@ -361,7 +361,7 @@
 ;; The future plan is to separate those properties from the block' content.
 (defn remove-built-in-properties
   [format content]
-  (let [trim-content (string/trim content)]
+  (let [trim-content (some-> content string/trim)]
     (if (or
          (and (= format :markdown)
               (string/starts-with? trim-content "```")
@@ -462,4 +462,4 @@
     (if (seq properties-order)
       (keep (fn [k] (when (contains? properties k) [k (get properties k)]))
             (distinct properties-order))
-      properties*)))
+      properties*)))