diff --git a/src/app/user_session.ts b/src/app/user_session.ts
index d3dfc1d..50e6a2b 100644
--- a/src/app/user_session.ts
+++ b/src/app/user_session.ts
@@ -23,7 +23,7 @@ const expireTicket = async (
   ctx: restate.RpcContext,
   userId: string,
   ticketId: string,
-) => { };
+) => {};
 
 const checkout = async (ctx: restate.RpcContext, userId: string) => {
   return true;
diff --git a/src/part2/ticket_service.ts b/src/part2/ticket_service.ts
index 37d0de3..d5ddeda 100644
--- a/src/part2/ticket_service.ts
+++ b/src/part2/ticket_service.ts
@@ -19,7 +19,7 @@ enum TicketStatus {
 
 const reserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Available) {
     ctx.set("status", TicketStatus.Reserved);
@@ -31,7 +31,7 @@ const reserve = async (ctx: restate.RpcContext) => {
 
 const unreserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Sold) {
     return false;
@@ -43,7 +43,7 @@ const unreserve = async (ctx: restate.RpcContext) => {
 
 const markAsSold = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Reserved) {
     ctx.set("status", TicketStatus.Sold);
diff --git a/src/part2/user_session.ts b/src/part2/user_session.ts
index 67e2316..50a271d 100644
--- a/src/part2/user_session.ts
+++ b/src/part2/user_session.ts
@@ -21,7 +21,7 @@ const addTicket = async (
   const reservationSuccess = await ctx.rpc(ticketServiceApi).reserve(ticketId);
 
   if (reservationSuccess) {
-    const tickets = (await ctx.get<string[]>("tickets")) || [];
+    const tickets = (await ctx.get<string[]>("tickets")) ?? [];
     tickets.push(ticketId);
     ctx.set("tickets", tickets);
 
@@ -38,7 +38,7 @@ const expireTicket = async (
   userId: string,
   ticketId: string,
 ) => {
-  const tickets = (await ctx.get<string[]>("tickets")) || [];
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
   const ticketIndex = tickets.findIndex((ticket) => ticket === ticketId);
 
@@ -51,9 +51,9 @@ const expireTicket = async (
 };
 
 const checkout = async (ctx: restate.RpcContext, userId: string) => {
-  const tickets = await ctx.get<string[]>("tickets");
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
-  if (tickets === null || tickets.length === 0) {
+  if (tickets.length === 0) {
     return false;
   }
 
diff --git a/src/part3/ticket_service.ts b/src/part3/ticket_service.ts
index 37d0de3..d5ddeda 100644
--- a/src/part3/ticket_service.ts
+++ b/src/part3/ticket_service.ts
@@ -19,7 +19,7 @@ enum TicketStatus {
 
 const reserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Available) {
     ctx.set("status", TicketStatus.Reserved);
@@ -31,7 +31,7 @@ const reserve = async (ctx: restate.RpcContext) => {
 
 const unreserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Sold) {
     return false;
@@ -43,7 +43,7 @@ const unreserve = async (ctx: restate.RpcContext) => {
 
 const markAsSold = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Reserved) {
     ctx.set("status", TicketStatus.Sold);
diff --git a/src/part3/user_session.ts b/src/part3/user_session.ts
index 0c430a8..1553e34 100644
--- a/src/part3/user_session.ts
+++ b/src/part3/user_session.ts
@@ -21,7 +21,7 @@ const addTicket = async (
   const reservationSuccess = await ctx.rpc(ticketServiceApi).reserve(ticketId);
 
   if (reservationSuccess) {
-    const tickets = (await ctx.get<string[]>("tickets")) || [];
+    const tickets = (await ctx.get<string[]>("tickets")) ?? [];
     tickets.push(ticketId);
     ctx.set("tickets", tickets);
 
@@ -38,7 +38,7 @@ const expireTicket = async (
   userId: string,
   ticketId: string,
 ) => {
-  const tickets = (await ctx.get<string[]>("tickets")) || [];
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
   const ticketIndex = tickets.findIndex((ticket) => ticket === ticketId);
 
@@ -51,9 +51,9 @@ const expireTicket = async (
 };
 
 const checkout = async (ctx: restate.RpcContext, userId: string) => {
-  const tickets = await ctx.get<string[]>("tickets");
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
-  if (tickets && tickets.length > 0) {
+  if (tickets.length > 0) {
     const checkout_success = await ctx
       .rpc(checkoutApi)
       .checkout({ userId: userId, tickets: tickets! });
diff --git a/src/part4/ticket_service.ts b/src/part4/ticket_service.ts
index 37d0de3..d5ddeda 100644
--- a/src/part4/ticket_service.ts
+++ b/src/part4/ticket_service.ts
@@ -19,7 +19,7 @@ enum TicketStatus {
 
 const reserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Available) {
     ctx.set("status", TicketStatus.Reserved);
@@ -31,7 +31,7 @@ const reserve = async (ctx: restate.RpcContext) => {
 
 const unreserve = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Sold) {
     return false;
@@ -43,7 +43,7 @@ const unreserve = async (ctx: restate.RpcContext) => {
 
 const markAsSold = async (ctx: restate.RpcContext) => {
   const status =
-    (await ctx.get<TicketStatus>("status")) || TicketStatus.Available;
+    (await ctx.get<TicketStatus>("status")) ?? TicketStatus.Available;
 
   if (status === TicketStatus.Reserved) {
     ctx.set("status", TicketStatus.Sold);
diff --git a/src/part4/user_session.ts b/src/part4/user_session.ts
index 84dba0c..0fe5f06 100644
--- a/src/part4/user_session.ts
+++ b/src/part4/user_session.ts
@@ -23,7 +23,7 @@ const addTicket = async (
 
   if (reservation_success) {
     // add ticket to user session tickets
-    const tickets = (await ctx.get<string[]>("tickets")) || [];
+    const tickets = (await ctx.get<string[]>("tickets")) ?? [];
     tickets.push(ticketId);
     ctx.set("tickets", tickets);
 
@@ -41,7 +41,7 @@ const expireTicket = async (
   userId: string,
   ticketId: string,
 ) => {
-  const tickets = (await ctx.get<string[]>("tickets")) || [];
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
   const index = tickets.findIndex((id) => id === ticketId);
 
@@ -55,9 +55,9 @@ const expireTicket = async (
 };
 
 const checkout = async (ctx: restate.RpcContext, userId: string) => {
-  const tickets = await ctx.get<string[]>("tickets");
+  const tickets = (await ctx.get<string[]>("tickets")) ?? [];
 
-  if (tickets && tickets.length > 0) {
+  if (tickets.length > 0) {
     const checkout_success = await ctx
       .rpc(checkoutApi)
       .checkout({ userId: userId, tickets: tickets! });