feat: mark not required string property as optional

npm/ng-packs/packages/schematics/src/utils/model.ts

@@ -1,5 +1,5 @@
 import { VOLO_NAME_VALUE, VOLO_REGEX } from '../constants';
-import { Interface, Model, Property, Type, TypeWithEnum } from '../models';
+import { Interface, Model, Property, PropertyDef, Type, TypeWithEnum } from '../models';
 import { parseNamespace } from './namespace';
 import { relativePathToModel } from './path';
 import { camel } from './text';
@@ -119,7 +119,7 @@ export function createImportRefToInterfaceReducerCreator(params: ModelGeneratorP
 
     typeDef.properties?.forEach(prop => {
       const name = camel(prop.name);
-      const optional = prop.typeSimple.endsWith('?') ? '?' : '';
+      const optional = isOptionalProperty(prop) ? '?' : '';
       const type = simplifyType(prop.typeSimple);
       const refs = parseType(prop.type).reduce(
         (acc: string[], r) => acc.concat(parseGenerics(r).toGenerics()),
@@ -150,3 +150,9 @@ export function createRefToImportReducerCreator(params: ModelGeneratorParams) {
   const { solution } = params;
   return (namespace: string) => createTypesToImportsReducer(solution, namespace);
 }
+
+function isOptionalProperty(prop: PropertyDef) {
+  return (
+    prop.typeSimple.endsWith('?') || (prop.typeSimple === 'string' && prop.isRequired === false)
+  );
+}