diff --git a/domain/src/main/kotlin/tw/waterballsa/gaas/domain/User.kt b/domain/src/main/kotlin/tw/waterballsa/gaas/domain/User.kt
index 7af6c449..54da89fb 100644
--- a/domain/src/main/kotlin/tw/waterballsa/gaas/domain/User.kt
+++ b/domain/src/main/kotlin/tw/waterballsa/gaas/domain/User.kt
@@ -16,6 +16,9 @@ class User(
         private const val NICKNAME_MAXIMUM_BYTE_SIZE = 16
     }
 
+    constructor(email: String, nickname: String, identities: MutableList<String> ) :
+            this(null, email, nickname, identities)
+
     fun changeNickname(nickname: String) {
         val nicknameByteSize = nickname.toByteArray().size
 
diff --git a/spring/src/main/kotlin/tw/waterballsa/gaas/spring/controllers/OAuth2Controller.kt b/spring/src/main/kotlin/tw/waterballsa/gaas/spring/controllers/OAuth2Controller.kt
index e0bdc802..5944a298 100644
--- a/spring/src/main/kotlin/tw/waterballsa/gaas/spring/controllers/OAuth2Controller.kt
+++ b/spring/src/main/kotlin/tw/waterballsa/gaas/spring/controllers/OAuth2Controller.kt
@@ -45,7 +45,7 @@ class OAuth2Controller(
 }
 
 val Jwt.email: String
-    get() = claims["email"]?.let { it as String }
+    get() = claims["email"]?.toString()
         ?: throw PlatformException("JWT email should exist.")
 
 val Jwt.identityProviderId: String
diff --git a/spring/src/test/kotlin/tw/waterballsa/gaas/spring/it/controllers/UserControllerTest.kt b/spring/src/test/kotlin/tw/waterballsa/gaas/spring/it/controllers/UserControllerTest.kt
index 54bba0ff..200abbd0 100644
--- a/spring/src/test/kotlin/tw/waterballsa/gaas/spring/it/controllers/UserControllerTest.kt
+++ b/spring/src/test/kotlin/tw/waterballsa/gaas/spring/it/controllers/UserControllerTest.kt
@@ -82,12 +82,12 @@ class UserControllerTest @Autowired constructor(
     }
 
     private fun givenUserNickname(nickname: String): User {
-        val user = User(null, "userA@example.com", nickname, mockUser.identities)
+        val user = User("userA@example.com", nickname, mockUser.identities)
         return userRepository.createUser(user)
     }
 
     private fun givenAnotherUserNickname(nickname: String): User {
-        val user = User(null, "userB@example.com", nickname, mockUser.identities)
+        val user = User("userB@example.com", nickname, mockUser.identities)
         return userRepository.createUser(user)
     }
 
@@ -103,7 +103,6 @@ class UserControllerTest @Autowired constructor(
                 .withJwt(toJwt())
         )
 
-
     private fun ResultActions.thenGetUserSuccessfully() {
         this.andExpect(status().isOk)
             .andExpect(jsonPath("$.id").value(mockUser.id!!.value))
@@ -119,10 +118,10 @@ class UserControllerTest @Autowired constructor(
     }
 
     private fun ResultActions.thenUserNicknameShouldBeChanged(nickname: String) {
-        val userViewModel = andExpect(status().isOk)
+        val user = andExpect(status().isOk)
             .getBody(UpdateUserViewModel::class.java)
 
-        userRepository.findById(userViewModel.id)
+        userRepository.findById(user.id)
             .also { assertThat(it).isNotNull }
             .also { assertThat(it!!.nickname).isEqualTo(nickname) }
     }