fix error log for cascader-panel

packages/cascader-panel/src/cascader-panel.vue

@@ -270,6 +270,7 @@ export default {
       }
     },
     handleExpand(node, silent) {
+      if (node) {
         const { activePath } = this;
         const { level } = node;
         const path = activePath.slice(0, level - 1);
@@ -291,6 +292,7 @@ export default {
             this.$emit('expand-change', pathValues);
           }
         }
+      }
     },
     handleCheckChange(value) {
       this.checkedValue = value;