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/GlobalExceptionHandler.java b/src/main/java/com/softserve/itacademy/exception/GlobalExceptionHandler.java
new file mode 100644
index 0000000..f1db39a
--- /dev/null
+++ b/src/main/java/com/softserve/itacademy/exception/GlobalExceptionHandler.java
@@ -0,0 +1,49 @@
+package com.softserve.itacademy.exception;
+
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ControllerAdvice;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.servlet.ModelAndView;
+
+import javax.persistence.EntityNotFoundException;
+import javax.servlet.http.HttpServletRequest;
+
+@Slf4j
+@ControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(NullEntityReferenceException.class)
+    @ResponseStatus(HttpStatus.BAD_REQUEST)
+    public ModelAndView handleNullEntityReferenceException(HttpServletRequest request, NullEntityReferenceException ex) {
+        return createModelAndView(request, HttpStatus.BAD_REQUEST, ex);
+    }
+
+    @ExceptionHandler(EntityNotFoundException.class)
+    @ResponseStatus(HttpStatus.NOT_FOUND)
+    public ModelAndView handleEntityNotFoundException(HttpServletRequest request, EntityNotFoundException ex) {
+        return createModelAndView(request, HttpStatus.NOT_FOUND, ex);
+    }
+
+    @ExceptionHandler(Exception.class)
+    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
+    public ModelAndView handleException(HttpServletRequest request, Exception ex) {
+        return createModelAndView(request, HttpStatus.INTERNAL_SERVER_ERROR, ex);
+    }
+
+    private static ModelAndView createModelAndView(HttpServletRequest request, HttpStatus httpStatus, Exception ex) {
+        log.error("An error occurred: \"{}\" at the specified URL: \"{}\".", ex.getMessage(), request.getRequestURI());
+        ModelAndView modelAndView = new ModelAndView(getView(httpStatus));
+        modelAndView.addObject("errorMessage", ex.getMessage());
+        return modelAndView;
+    }
+
+    private static String getView(HttpStatus httpStatus) {
+        switch (httpStatus) {
+            case BAD_REQUEST: return "400";
+            case NOT_FOUND: return "404";
+            default: return "500";
+        }
+    }
+}
\ No newline at end of file
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..046d99b
--- /dev/null
+++ b/src/main/java/com/softserve/itacademy/exception/NullEntityReferenceException.java
@@ -0,0 +1,13 @@
+package com.softserve.itacademy.exception;
+
+
+public class NullEntityReferenceException extends RuntimeException {
+
+    public NullEntityReferenceException() {
+        super();
+    }
+
+    public NullEntityReferenceException(String message) {
+        super(message);
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/softserve/itacademy/service/RoleService.java b/src/main/java/com/softserve/itacademy/service/RoleService.java
index 6b44062..68ef711 100644
--- a/src/main/java/com/softserve/itacademy/service/RoleService.java
+++ b/src/main/java/com/softserve/itacademy/service/RoleService.java
@@ -1,13 +1,15 @@
 package com.softserve.itacademy.service;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.Role;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.List;
 
 public interface RoleService {
-    Role create(Role role);
-    Role readById(long id);
-    Role update(Role role);
-    void delete(long id);
+    Role create(Role role) throws NullEntityReferenceException;
+    Role readById(long id) throws EntityNotFoundException;
+    Role update(Role role) throws NullEntityReferenceException, EntityNotFoundException;
+    void delete(long id) throws EntityNotFoundException;
     List<Role> getAll();
 }
diff --git a/src/main/java/com/softserve/itacademy/service/StateService.java b/src/main/java/com/softserve/itacademy/service/StateService.java
index 1449fb7..d23cae7 100644
--- a/src/main/java/com/softserve/itacademy/service/StateService.java
+++ b/src/main/java/com/softserve/itacademy/service/StateService.java
@@ -1,15 +1,19 @@
 package com.softserve.itacademy.service;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.State;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.List;
 
 public interface StateService {
-    State create(State state);
-    State readById(long id);
-    State update(State state);
-    void delete(long id);
 
-    State getByName(String name);
+    State create(State state) throws NullEntityReferenceException;
+    State readById(long id) throws EntityNotFoundException;
+    State update(State state) throws NullEntityReferenceException, EntityNotFoundException;
+    void delete(long id) throws EntityNotFoundException;
+
+    State getByName(String name) throws EntityNotFoundException;
     List<State> getAll();
+
 }
diff --git a/src/main/java/com/softserve/itacademy/service/TaskService.java b/src/main/java/com/softserve/itacademy/service/TaskService.java
index b6e4318..74538f8 100644
--- a/src/main/java/com/softserve/itacademy/service/TaskService.java
+++ b/src/main/java/com/softserve/itacademy/service/TaskService.java
@@ -1,15 +1,19 @@
 package com.softserve.itacademy.service;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.Task;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.List;
 
 public interface TaskService {
-    Task create(Task task);
-    Task readById(long id);
-    Task update(Task task);
-    void delete(long id);
+
+    Task create(Task task) throws NullEntityReferenceException;
+    Task readById(long id) throws EntityNotFoundException;
+    Task update(Task task) throws NullEntityReferenceException, EntityNotFoundException;
+    void delete(long id) throws EntityNotFoundException;
 
     List<Task> getAll();
     List<Task> getByTodoId(long todoId);
+
 }
diff --git a/src/main/java/com/softserve/itacademy/service/ToDoService.java b/src/main/java/com/softserve/itacademy/service/ToDoService.java
index 5c57637..d786ca1 100644
--- a/src/main/java/com/softserve/itacademy/service/ToDoService.java
+++ b/src/main/java/com/softserve/itacademy/service/ToDoService.java
@@ -1,14 +1,17 @@
 package com.softserve.itacademy.service;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.ToDo;
 
+import javax.persistence.EntityNotFoundException;
+import javax.validation.constraints.Null;
 import java.util.List;
 
 public interface ToDoService {
-    ToDo create(ToDo todo);
-    ToDo readById(long id);
-    ToDo update(ToDo todo);
-    void delete(long id);
+    ToDo create(ToDo todo) throws NullEntityReferenceException;
+    ToDo readById(long id) throws EntityNotFoundException;
+    ToDo update(ToDo todo) throws NullEntityReferenceException, EntityNotFoundException;
+    void delete(long id) throws EntityNotFoundException;
 
     List<ToDo> getAll();
     List<ToDo> getByUserId(long userId);
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..952522b 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/RoleServiceImpl.java
@@ -1,42 +1,53 @@
 package com.softserve.itacademy.service.impl;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 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 javax.persistence.EntityNotFoundException;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Optional;
 
 @Service
+@RequiredArgsConstructor
 public class RoleServiceImpl implements RoleService {
 
-    private RoleRepository roleRepository;
+    private static final String ROLE_CANNOT_BE_NULL = "Role cannot be null";
+    private static final String ROLE_NOT_FOUND = "Role not found";
+    private static final String ROLE_NOT_FOUND_WITH_ID = "Role not found with id ";
 
-    public RoleServiceImpl(RoleRepository roleRepository) {
-        this.roleRepository = roleRepository;
-    }
+    private final RoleRepository roleRepository;
 
     @Override
-    public Role create(Role role) {
-            return roleRepository.save(role);
+    public Role create(Role role) throws NullEntityReferenceException {
+        if (role == null){
+            throw new NullEntityReferenceException(ROLE_CANNOT_BE_NULL);
+        }
+        return roleRepository.save(role);
     }
 
     @Override
-    public Role readById(long id) {
-        Optional<Role> optional = roleRepository.findById(id);
-            return optional.get();
+    public Role readById(long id) throws EntityNotFoundException {
+       return roleRepository.findById(id)
+               .orElseThrow(() -> new EntityNotFoundException(ROLE_NOT_FOUND));
     }
 
     @Override
-    public Role update(Role role) {
-            Role oldRole = readById(role.getId());
-                return roleRepository.save(role);
+    public Role update(Role role) throws EntityNotFoundException, NullEntityReferenceException {
+        if (role == null){
+            throw new NullEntityReferenceException(ROLE_CANNOT_BE_NULL);
+        }
+        if (!roleRepository.existsById(role.getId())){
+            throw new EntityNotFoundException(ROLE_NOT_FOUND_WITH_ID + role.getId());
+        }
+        return roleRepository.save(role);
     }
 
     @Override
-    public void delete(long id) {
+    public void delete(long id) throws EntityNotFoundException {
         Role role = readById(id);
             roleRepository.delete(role);
     }
diff --git a/src/main/java/com/softserve/itacademy/service/impl/StateServiceImpl.java b/src/main/java/com/softserve/itacademy/service/impl/StateServiceImpl.java
index ac95e84..cd4026a 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/StateServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/StateServiceImpl.java
@@ -1,49 +1,62 @@
 package com.softserve.itacademy.service.impl;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.State;
 import com.softserve.itacademy.repository.StateRepository;
 import com.softserve.itacademy.service.StateService;
 import org.springframework.stereotype.Service;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 
 @Service
 public class StateServiceImpl implements StateService {
-    private StateRepository stateRepository;
+
+    private static final String NULL_ENTITY_EXCEPTION_MESSAGE = "The passed State object cannot be null.";
+
+    private final StateRepository stateRepository;
 
     public StateServiceImpl(StateRepository stateRepository) {
         this.stateRepository = stateRepository;
     }
 
     @Override
-    public State create(State state) {
-            return stateRepository.save(state);
+    public State create(State state) throws NullEntityReferenceException {
+        if(state == null) {
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION_MESSAGE);
+        }
+
+        return stateRepository.save(state);
     }
 
     @Override
-    public State readById(long id) {
-        Optional<State> optional = stateRepository.findById(id);
-            return optional.get();
+    public State readById(long id) throws EntityNotFoundException {
+        return stateRepository.findById(id)
+                .orElseThrow(() -> new EntityNotFoundException(String.format("An object of class State could not be found by the specified identifier \"%d\".", id)));
     }
 
     @Override
-    public State update(State state) {
-            State oldState = readById(state.getId());
-                return stateRepository.save(state);
+    public State update(State state) throws NullEntityReferenceException, EntityNotFoundException {
+        if(state == null) {
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION_MESSAGE);
+        }
+
+        readById(state.getId());
+        return stateRepository.save(state);
     }
 
     @Override
-    public void delete(long id) {
+    public void delete(long id) throws EntityNotFoundException {
         State state = readById(id);
-            stateRepository.delete(state);
+        stateRepository.delete(state);
     }
 
     @Override
-    public State getByName(String name) {
-        Optional<State> optional = Optional.ofNullable(stateRepository.getByName(name));
-            return optional.get();
+    public State getByName(String name) throws EntityNotFoundException {
+        return Optional.ofNullable(stateRepository.getByName(name))
+                .orElseThrow(() -> new EntityNotFoundException(String.format("An object of class State could not be found by the specified name \"%s\".", name)));
     }
 
     @Override
@@ -51,4 +64,5 @@ public List<State> getAll() {
         List<State> states = stateRepository.getAll();
         return states.isEmpty() ? new ArrayList<>() : states;
     }
+
 }
diff --git a/src/main/java/com/softserve/itacademy/service/impl/TaskServiceImpl.java b/src/main/java/com/softserve/itacademy/service/impl/TaskServiceImpl.java
index 6161dc8..a40561f 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/TaskServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/TaskServiceImpl.java
@@ -1,43 +1,56 @@
 package com.softserve.itacademy.service.impl;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.Task;
 import com.softserve.itacademy.repository.TaskRepository;
 import com.softserve.itacademy.service.TaskService;
 import org.springframework.stereotype.Service;
 
+import javax.persistence.EntityNotFoundException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 
 @Service
 public class TaskServiceImpl implements TaskService {
-    private TaskRepository taskRepository;
+
+    private static final String NULL_ENTITY_EXCEPTION_MESSAGE = "The passed Task object cannot be null.";
+
+    private final TaskRepository taskRepository;
 
     public TaskServiceImpl(TaskRepository taskRepository) {
         this.taskRepository = taskRepository;
     }
 
     @Override
-    public Task create(Task user) {
-            return taskRepository.save(user);
+    public Task create(Task user) throws NullEntityReferenceException {
+        if(user == null) {
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION_MESSAGE);
+        }
+
+        return taskRepository.save(user);
     }
 
     @Override
-    public Task readById(long id) {
-        Optional<Task> optional = taskRepository.findById(id);
-            return optional.get();
+    public Task readById(long id) throws EntityNotFoundException {
+        return taskRepository.findById(id)
+                .orElseThrow(() -> new EntityNotFoundException(String.format("An object of class Task could not be found by the specified identifier \"%d\".", id)));
     }
 
     @Override
-    public Task update(Task task) {
-            Task oldTask = readById(task.getId());
-                return taskRepository.save(task);
+    public Task update(Task task) throws NullEntityReferenceException, EntityNotFoundException {
+        if(task == null) {
+            throw new NullEntityReferenceException(NULL_ENTITY_EXCEPTION_MESSAGE);
+        }
+
+        readById(task.getId());
+        return taskRepository.save(task);
     }
 
     @Override
-    public void delete(long id) {
+    public void delete(long id) throws EntityNotFoundException {
         Task task = readById(id);
-            taskRepository.delete(task);
+        taskRepository.delete(task);
     }
 
     @Override
diff --git a/src/main/java/com/softserve/itacademy/service/impl/ToDoServiceImpl.java b/src/main/java/com/softserve/itacademy/service/impl/ToDoServiceImpl.java
index d000571..d29705b 100644
--- a/src/main/java/com/softserve/itacademy/service/impl/ToDoServiceImpl.java
+++ b/src/main/java/com/softserve/itacademy/service/impl/ToDoServiceImpl.java
@@ -1,10 +1,13 @@
 package com.softserve.itacademy.service.impl;
 
+import com.softserve.itacademy.exception.NullEntityReferenceException;
 import com.softserve.itacademy.model.ToDo;
 import com.softserve.itacademy.repository.ToDoRepository;
 import com.softserve.itacademy.service.ToDoService;
 import org.springframework.stereotype.Service;
 
+import javax.persistence.EntityNotFoundException;
+import javax.validation.constraints.Null;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
@@ -20,19 +23,27 @@ public ToDoServiceImpl(ToDoRepository todoRepository) {
 
     @Override
     public ToDo create(ToDo todo) {
+        if (todo == null) {
+            throw new NullEntityReferenceException("ToDo cannot be null");
+        }
             return todoRepository.save(todo);
     }
 
     @Override
     public ToDo readById(long id) {
         Optional<ToDo> optional = todoRepository.findById(id);
-            return optional.get();
+            return optional.orElseThrow(() -> new EntityNotFoundException("ToDO not found with id " + id));
     }
 
     @Override
     public ToDo update(ToDo todo) {
-            ToDo oldTodo = readById(todo.getId());
-                return todoRepository.save(todo);
+        if (todo == null) {
+            throw new NullEntityReferenceException("ToDo cannot be null");
+        }
+        if (!todoRepository.existsById(todo.getId())) {
+            throw new EntityNotFoundException("ToDo not found with id " + todo.getId());
+        }
+        return todoRepository.save(todo);
     }
 
     @Override
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="${errorMessage}"></p>
+        </div>
+        <a href="/home">Go to Home page </a>
+    </div>
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/500.html b/src/main/resources/templates/500.html
new file mode 100644
index 0000000..05dba3b
--- /dev/null
+++ b/src/main/resources/templates/500.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport"
+          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
+    <meta http-equiv="X-UA-Compatible" content="ie=edge">
+    <title>500 Internal Server Error</title>
+</head>
+<body>
+<div class="container">
+    <div class="text-center">
+        <h1 class="display-4">500 Internal Server Error</h1>
+
+        <p th:if="${errorMessage}" class="lead text-danger">
+            <strong th:text="${errorMessage}"></strong>
+        </p>
+    </div>
+</div>
+</body>
+</html>
\ No newline at end of file