fix(plugin): fix optional props in strict mode

lib/plugin/utils/plugin-utils.ts

@@ -62,6 +62,12 @@ export function getTypeReferenceAsString(
     if (text === Date.name) {
       return text;
     }
+    if (isAutoGeneratedUnion(type)) {
+      return getTypeReferenceAsString(
+        type.types[type.types.length - 1],
+        typeChecker
+      );
+    }
     if (
       text === 'any' ||
       text === 'unknown' ||
@@ -138,3 +144,21 @@ export function replaceImportPath(typeReference: string, fileName: string) {
 export function isDynamicallyAdded(identifier: ts.Node) {
   return identifier && !identifier.parent && identifier.pos === -1;
 }
+
+/**
+ * when "strict" mode enabled, TypeScript transform the type signature of optional properties to
+ * the {undefined | T} where T is the original type. Hence, we have to extract the last type of type union
+ * @param type
+ */
+export function isAutoGeneratedUnion(
+  type: ts.Type
+): type is ts.UnionOrIntersectionType {
+  if (type.isUnionOrIntersection() && !isEnum(type)) {
+    if (type.types && type.types.length === 2) {
+      if (type.types.some((type: any) => type.intrinsicName === 'undefined')) {
+        return true;
+      }
+    }
+  }
+  return false;
+}

test/plugin/fixtures/create-cat-alt.dto.ts

@@ -20,7 +20,7 @@ export class CreateCatDto2 {
   age: number = 3;
   tags: string[];
   status: Status = Status.ENABLED;
-  readonly breed?: string;
+  readonly breed?: string | undefined;
   nodes: Node[];
   alias: AliasedType;
   numberAlias: NumberAlias;