diff --git a/plugin/kintone-addins/src/actions/cascading-dropdown-selectors.ts b/plugin/kintone-addins/src/actions/cascading-dropdown-selectors.ts
index 5820eef..ea84ae1 100644
--- a/plugin/kintone-addins/src/actions/cascading-dropdown-selectors.ts
+++ b/plugin/kintone-addins/src/actions/cascading-dropdown-selectors.ts
@@ -121,8 +121,8 @@ namespace DropDownConfig {
             value: fieldData.value,
             index: fieldCodeToIndexMap.get(fieldCode),
           }))
-          .filter((item) => item.index !== undefined)
-          .sort((a, b) => a.index - b.index)
+          .filter((item) => item.index !== undefined || item.index !== null)
+          .sort((a, b) => a.index! - b.index!)
       )
       .forEach((recordArray) => {
         recordArray.forEach((item, i, array) => {
@@ -133,7 +133,7 @@ namespace DropDownConfig {
           if (index === 0) {
             tempDictionary["0_TOP"].add(v);
           } else {
-            const previousItem = array[index - 1];
+            const previousItem = array[index! - 1];
             const previousKey = `${previousItem.index}_${previousItem.value}`;
             tempDictionary[previousKey] =
               tempDictionary[previousKey] || new Set();
@@ -250,7 +250,7 @@ export class CascadingDropDownAction implements IAction {
     DropdownContainer.addSaveBtnEvent(
       pageType === "app"
         ? tableElement
-        : document.getElementById("appForm-gaia")
+        : document.getElementById("appForm-gaia")!
     );
     DropdownContainer.render(tableElement);
   }
@@ -371,9 +371,7 @@ namespace DropdownContainer {
   ): void => {
     let select;
     if (!initSelect) {
-      select = selects
-        .get(fieldCode)
-        .querySelector<HTMLSelectElement>("select");
+      select = selects.get(fieldCode)?.querySelector<HTMLSelectElement>("select");
       if (!select) {
         console.error(
           `フィールド ${fieldCode} のドロップダウンメニュー要素が見つかりません`
@@ -383,7 +381,7 @@ namespace DropdownContainer {
       }
     } else {
       select = initSelect;
-      state[fieldCode] = value;
+      state[fieldCode] = value!;
     }
 
     const field = fieldList.find((f) => f.dropDown.code === fieldCode);
@@ -421,7 +419,7 @@ namespace DropdownContainer {
         const fieldCode = field.dropDown.code;
         updateOptions(fieldCode);
         (
-          selects.get(fieldCode).previousElementSibling as HTMLInputElement
+          selects.get(fieldCode)?.previousElementSibling as HTMLInputElement
         ).value = "";
         delete state[fieldCode];
       });