diff --git a/__tests__/SelfMailerModels.unit.ts b/__tests__/SelfMailerModels.unit.ts
index dba39d0..17156de 100755
--- a/__tests__/SelfMailerModels.unit.ts
+++ b/__tests__/SelfMailerModels.unit.ts
@@ -91,7 +91,7 @@ describe("SelfMailer Models", () => {
 
     it("rejects invalid values for outside_template_id", () => {
       const rec = new SelfMailer();
-      expect(rec.outside_template_id).toBeNull();
+      expect(rec.outside_template_id).toBeUndefined();
 
       const invalidValues = ["Nope"];
       for (const val of invalidValues) {
@@ -106,7 +106,7 @@ describe("SelfMailer Models", () => {
 
     it("rejects invalid values for outside_template_id", () => {
       const rec = new SelfMailer();
-      expect(rec.inside_template_id).toBeNull();
+      expect(rec.inside_template_id).toBeUndefined();
 
       const invalidValues = ["Nope"];
       for (const val of invalidValues) {
@@ -121,7 +121,7 @@ describe("SelfMailer Models", () => {
 
     it("rejects invalid values for outside_template_version_id", () => {
       const rec = new SelfMailer();
-      expect(rec.outside_template_version_id).toBeNull();
+      expect(rec.outside_template_version_id).toBeUndefined();
 
       const invalidValues = ["Nope"];
       for (const val of invalidValues) {
@@ -138,7 +138,7 @@ describe("SelfMailer Models", () => {
 
     it("rejects invalid values for inside_template_version_id", () => {
       const rec = new SelfMailer();
-      expect(rec.inside_template_version_id).toBeNull();
+      expect(rec.inside_template_version_id).toBeUndefined();
 
       const invalidValues = ["Nope"];
       for (const val of invalidValues) {
diff --git a/models/self-mailer.ts b/models/self-mailer.ts
index 3c59bca..c00e73e 100644
--- a/models/self-mailer.ts
+++ b/models/self-mailer.ts
@@ -154,9 +154,9 @@ export class SelfMailer {
    * @type {string}
    * @memberof SelfMailer
    */
-  private "_outside_template_id": string | null;
+  private "_outside_template_id"?: string | null;
   public get outside_template_id() {
-    return this._outside_template_id || null;
+    return (this._outside_template_id || null || undefined) as string;
   }
   public set outside_template_id(newValue: string | null) {
     if (newValue && !/^tmpl_[a-zA-Z0-9]+$/.test(newValue)) {
@@ -170,9 +170,9 @@ export class SelfMailer {
    * @type {string}
    * @memberof SelfMailer
    */
-  private "_inside_template_id": string | null;
+  private "_inside_template_id"?: string | null;
   public get inside_template_id() {
-    return this._inside_template_id || null;
+    return (this._inside_template_id || null || undefined) as string;
   }
   public set inside_template_id(newValue: string | null) {
     if (newValue && !/^tmpl_[a-zA-Z0-9]+$/.test(newValue)) {
@@ -186,9 +186,9 @@ export class SelfMailer {
    * @type {string}
    * @memberof SelfMailer
    */
-  private "_outside_template_version_id": string | null;
+  private "_outside_template_version_id"?: string | null;
   public get outside_template_version_id() {
-    return this._outside_template_version_id || null;
+    return (this._outside_template_version_id || null || undefined) as string;
   }
   public set outside_template_version_id(newValue: string | null) {
     if (newValue && !/^vrsn_[a-zA-Z0-9]+$/.test(newValue)) {
@@ -202,9 +202,9 @@ export class SelfMailer {
    * @type {string}
    * @memberof SelfMailer
    */
-  private "_inside_template_version_id": string | null;
+  private "_inside_template_version_id"?: string | null;
   public get inside_template_version_id() {
-    return this._inside_template_version_id || null;
+    return (this._inside_template_version_id || null || undefined) as string;
   }
   public set inside_template_version_id(newValue: string | null) {
     if (newValue && !/^vrsn_[a-zA-Z0-9]+$/.test(newValue)) {