fixes

react-openapi/src/components/fields/renderers/DiscriminatorField.tsx

@@ -15,13 +15,21 @@ export function DiscriminatorField({ field, value, onChange, error }: Props) {
   const discProp = field.discriminatorProperty ?? "type";
   const currentType = value?.[discProp] ?? "";
 
+  function defaultFieldValue(field: FieldConfig): any {
+    if (field.enumValues) return field.enumValues[0];
+    if (field.isArray) return [];
+    if (field.type === "object") return {};
+    if (field.type === "number" || field.type === "integer") return 0;
+    return null;
+  }
+
   const handleTypeChange = useCallback((e: any) => {
     const newType = e.target.value;
     const option = options.find((o) => o.value === newType);
     const newValue: Record<string, any> = { [discProp]: newType };
     if (option) {
       for (const f of option.fields) {
-        newValue[f.name] = f.enumValues?.[0] ?? f.type === "number" ? 0 : f.type === "integer" ? 0 : "";
+        newValue[f.name] = defaultFieldValue(f);
       }
     }
     onChange(newValue);