diff --git a/README.md b/README.md
index 40c3372..5fa0a49 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+[![Review Assignment Due Date](https://classroom.github.com/assets/deadline-readme-button-22041afd0340ce965d47ae6ef1cefeee28c7c493a6346c4f15d667ab976d596c.svg)](https://classroom.github.com/a/fcC7yEpn)
 # Java Online Marathon
 ## To-Do List Project
 1. Implement exception handling for custom exception.
diff --git a/src/main/java/com/softserve/itacademy/exception/NullEntityReferenceException.java b/src/main/java/com/softserve/itacademy/exception/NullEntityReferenceException.java
new file mode 100644
index 0000000..7fd1f9f
--- /dev/null
+++ b/src/main/java/com/softserve/itacademy/exception/NullEntityReferenceException.java
@@ -0,0 +1,11 @@
+package com.softserve.itacademy.exception;
+
+public class NullEntityReferenceException extends RuntimeException {
+    public NullEntityReferenceException() {
+        super();
+    }
+
+    public NullEntityReferenceException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java b/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java
index 7d517c6..c2c39d3 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java
@@ -3,6 +3,7 @@
 import com.softserve.itacademy.model.Role;
 import com.softserve.itacademy.repository.RoleRepository;
 import com.softserve.itacademy.service.RoleService;
+import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 
 import java.util.ArrayList;
@@ -10,13 +11,10 @@
 import java.util.Optional;
 
 @Service
+@RequiredArgsConstructor
 public class RoleServiceImpl implements RoleService {
 
-    private RoleRepository roleRepository;
-
-    public RoleServiceImpl(RoleRepository roleRepository) {
-        this.roleRepository = roleRepository;
-    }
+    private final RoleRepository roleRepository;
 
     @Override
     public Role create(Role role) {
diff --git a/src/main/java/com/softserve/itacademy/service/impl/UserServiceImpl.java b/src/main/java/com/softserve/itacademy/service/impl/UserServiceImpl.java
index 5b3645f..a966c37 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/UserServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/UserServiceImpl.java
@@ -1,10 +1,12 @@
 package com.softserve.itacademy.service.impl;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.User;
 import com.softserve.itacademy.repository.UserRepository;
 import com.softserve.itacademy.service.UserService;
 import org.springframework.stereotype.Service;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
@@ -12,6 +14,9 @@
 @Service
 public class UserServiceImpl implements UserService {
 
+    private static final String NULL_ENTITY_EXCEPTION = "Reference to an entity is null";
+    private static final String ENTITY_NOT_FOUND_EXCEPTION = "Reference to an entity is not found";
+
     private UserRepository userRepository;
 
     public UserServiceImpl(UserRepository userRepository) {
@@ -20,23 +25,36 @@ public UserServiceImpl(UserRepository userRepository) {
 
     @Override
     public User create(User user) {
+        if(user == null){
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION);
+        }
+
             return userRepository.save(user);
     }
 
     @Override
     public User readById(long id) {
+        if(!userRepository.existsById(id)){
+            throw new EntityNotFoundException(ENTITY_NOT_FOUND_EXCEPTION);
+        }
         Optional<User> optional = userRepository.findById(id);
             return optional.get();
     }
 
     @Override
     public User update(User user) {
+        if(user == null){
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION);
+        }
             User oldUser = readById(user.getId());
                 return userRepository.save(user);
     }
 
     @Override
     public void delete(long id) {
+        if(!userRepository.existsById(id)){
+            throw new EntityNotFoundException(ENTITY_NOT_FOUND_EXCEPTION);
+        }
         User user = readById(id);
             userRepository.delete(user);
     }
diff --git a/src/main/resources/templates/400.html b/src/main/resources/templates/400.html
new file mode 100644
index 0000000..76140ac
--- /dev/null
+++ b/src/main/resources/templates/400.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport"
+          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
+    <meta http-equiv="X-UA-Compatible" content="ie=edge">
+    <title>400 Bad Request</title>
+</head>
+<body>
+<div class="container">
+    <div class="text-center">
+        <h1 class="display-4">400 Bad Request</h1>
+
+        <p th:if="${errorMessage}" class="lead text-danger">
+            <strong th:text="${errorMessage}"></strong>
+        </p>
+    </div>
+</div>
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/404.html b/src/main/resources/templates/404.html
new file mode 100644
index 0000000..e67b843
--- /dev/null
+++ b/src/main/resources/templates/404.html
@@ -0,0 +1,29 @@
+<!doctype html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet">
+    <meta name="viewport"
+          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
+    <meta http-equiv="X-UA-Compatible" content="ie=edge">
+    <meta http-equiv="refresh" content="5;url=/" />
+    <title>Page Not Found</title>
+    <script>
+        setTimeout(function() {
+            window.location.href = '/home';
+        }, 5000);
+    </script>
+</head>
+<body class="d-flex flex-column min-vh-100">
+    <div class="container text-center my-auto">
+        <h1 class="display-4">404 Page Not Found</h1>
+        <div th:if="${errorMessage == null or errorMessage.isEmpty()}">
+            <p class="lead">Sorry, the page you are looking for does not exist. You will be redirected to the home page in 5 seconds.</p>
+        </div>
+        <div th:if="${errorMessage != null and !errorMessage.isEmpty()}">
+            <p class="text-danger" th:text="${errorMessage}"></p>
+        </div>
+        <a href="/home">Go to Home page </a>
+    </div>
+</body>
+</html>
\ No newline at end of file