diff --git a/client/src/data/template.ts b/client/src/data/template.ts
index d445b573..1ae39bd5 100644
--- a/client/src/data/template.ts
+++ b/client/src/data/template.ts
@@ -27,9 +27,9 @@ export interface OptionInterface {
    * Dialog(enable=...) annotation or dead end) disables the whole subtree of
    * an instance of this option. */
   enable?: any; // { modelicaPath: string; expression: string };
-  modifiers: any;
-  choiceModifiers?: { [key: string]: Modifiers };
-  treeList: string[];
+  modifiers?: any;
+  choiceModifiers?: { [key: string]: Modifiers | undefined };
+  treeList?: string[];
   definition: boolean;
   shortExclType: boolean; // Short class definition excluding `type` definition
   replaceable: boolean;
diff --git a/client/src/interpreter/interpreter.ts b/client/src/interpreter/interpreter.ts
index e2045aea..1ff90e36 100644
--- a/client/src/interpreter/interpreter.ts
+++ b/client/src/interpreter/interpreter.ts
@@ -32,7 +32,7 @@ export const constructSelectionPath = (
 };
 
 interface Modifier {
-  expression: Expression;
+  expression?: Expression | string;
   final: boolean;
   fromClassDefinition: boolean;
   redeclare?: string; // the redeclared type path, undefined if not a redeclare
@@ -660,7 +660,7 @@ export const evaluate = (
 const addToModObject = (
   newMods: {
     [key: string]: {
-      expression: Expression;
+      expression?: Expression | string;
       final: boolean;
       redeclare?: string;
       recordBinding?: boolean;
@@ -727,7 +727,7 @@ const getReplaceableType = (
   option: OptionInterface,
   mods: {
     [key: string]: {
-      expression: Expression;
+      expression?: Expression | string;
       final: boolean;
       redeclare?: string;
     };
@@ -808,7 +808,7 @@ const buildModsHelper = (
   const childOptions = option.options;
 
   const optionsWithModsList: string[] =
-    "treeList" in option && option.treeList.length > 0
+    option.treeList && option.treeList.length > 0
       ? option.treeList
       : [option.modelicaPath];
 
diff --git a/client/src/utils/modifier-helpers.ts b/client/src/utils/modifier-helpers.ts
index 74d18239..550df465 100644
--- a/client/src/utils/modifier-helpers.ts
+++ b/client/src/utils/modifier-helpers.ts
@@ -13,7 +13,11 @@ export interface ConfigValues {
 }
 
 export type Modifiers = {
-  [key: string]: { expression: Expression; final: boolean; redeclare?: string };
+  [key: string]: {
+    expression?: Expression | string;
+    final: boolean;
+    redeclare?: string;
+  };
 };
 
 function addToModObject(
@@ -289,10 +293,10 @@ export function getUpdatedModifiers(
       const instancePath =
         key.split("-")[1]?.split(".").slice(0, -1).join(".") || "";
       const option = allOptions[modelicaPath] as OptionInterface;
-      let choiceModifiers = {};
+      let choiceModifiers: Modifiers = {};
 
       if (option?.choiceModifiers) {
-        choiceModifiers = option?.choiceModifiers[value];
+        choiceModifiers = option?.choiceModifiers[value] || {};
         // take modifiers and change to instace keys, instancePath above and add to updatedModifiers as the last item.
       }