diff --git a/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxRoom.kt b/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxRoom.kt
index 96f2de9cdc..bc0a866117 100644
--- a/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxRoom.kt
+++ b/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxRoom.kt
@@ -57,7 +57,8 @@ class RxRoom(private val room: Room) {
         room.loadRoomMembersIfNeeded(MatrixCallbackSingle(it)).toSingle(it)
     }
 
-    fun joinRoom(reason: String?, viaServers: List<String> = emptyList()): Single<Unit> = Single.create {
+    fun joinRoom(reason: String? = null,
+                 viaServers: List<String> = emptyList()): Single<Unit> = Single.create {
         room.join(reason, viaServers, MatrixCallbackSingle(it)).toSingle(it)
     }
 
diff --git a/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxSession.kt b/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxSession.kt
index 1ef1c8cadb..5a42dbb804 100644
--- a/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxSession.kt
+++ b/matrix-sdk-android-rx/src/main/java/im/vector/matrix/rx/RxSession.kt
@@ -76,7 +76,9 @@ class RxSession(private val session: Session) {
         session.searchUsersDirectory(search, limit, excludedUserIds, MatrixCallbackSingle(it)).toSingle(it)
     }
 
-    fun joinRoom(roomId: String, reason: String?, viaServers: List<String> = emptyList()): Single<Unit> = Single.create {
+    fun joinRoom(roomId: String,
+                 reason: String? = null,
+                 viaServers: List<String> = emptyList()): Single<Unit> = Single.create {
         session.joinRoom(roomId, reason, viaServers, MatrixCallbackSingle(it)).toSingle(it)
     }
 }
diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomDirectoryService.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomDirectoryService.kt
index 8d03c70efa..c0e413f83b 100644
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomDirectoryService.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomDirectoryService.kt
@@ -30,12 +30,16 @@ interface RoomDirectoryService {
     /**
      * Get rooms from directory
      */
-    fun getPublicRooms(server: String?, publicRoomsParams: PublicRoomsParams, callback: MatrixCallback<PublicRoomsResponse>): Cancelable
+    fun getPublicRooms(server: String?,
+                       publicRoomsParams: PublicRoomsParams,
+                       callback: MatrixCallback<PublicRoomsResponse>): Cancelable
 
     /**
      * Join a room by id
      */
-    fun joinRoom(roomId: String, reason: String?, callback: MatrixCallback<Unit>): Cancelable
+    fun joinRoom(roomId: String,
+                 reason: String? = null,
+                 callback: MatrixCallback<Unit>): Cancelable
 
     /**
      * Fetches the overall metadata about protocols supported by the homeserver.
diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomService.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomService.kt
index 71a9a8e4fa..98abce5898 100644
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomService.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/RoomService.kt
@@ -30,7 +30,8 @@ interface RoomService {
     /**
      * Create a room asynchronously
      */
-    fun createRoom(createRoomParams: CreateRoomParams, callback: MatrixCallback<String>): Cancelable
+    fun createRoom(createRoomParams: CreateRoomParams,
+                   callback: MatrixCallback<String>): Cancelable
 
     /**
      * Join a room by id
@@ -39,7 +40,7 @@ interface RoomService {
      * @param viaServers the servers to attempt to join the room through. One of the servers must be participating in the room.
      */
     fun joinRoom(roomId: String,
-                 reason: String?,
+                 reason: String? = null,
                  viaServers: List<String> = emptyList(),
                  callback: MatrixCallback<Unit>): Cancelable
 
@@ -71,5 +72,6 @@ interface RoomService {
     /**
      * Mark all rooms as read
      */
-    fun markAllAsRead(roomIds: List<String>, callback: MatrixCallback<Unit>): Cancelable
+    fun markAllAsRead(roomIds: List<String>,
+                      callback: MatrixCallback<Unit>): Cancelable
 }
diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/members/MembershipService.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/members/MembershipService.kt
index 0f487880b7..b750c5347e 100644
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/members/MembershipService.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/session/room/members/MembershipService.kt
@@ -52,16 +52,21 @@ interface MembershipService {
     /**
      * Invite a user in the room
      */
-    fun invite(userId: String, reason: String?, callback: MatrixCallback<Unit>): Cancelable
+    fun invite(userId: String,
+               reason: String? = null,
+               callback: MatrixCallback<Unit>): Cancelable
 
     /**
      * Join the room, or accept an invitation.
      */
 
-    fun join(reason: String?, viaServers: List<String> = emptyList(), callback: MatrixCallback<Unit>): Cancelable
+    fun join(reason: String? = null,
+             viaServers: List<String> = emptyList(),
+             callback: MatrixCallback<Unit>): Cancelable
 
     /**
      * Leave the room, or reject an invitation.
      */
-    fun leave(reason: String?, callback: MatrixCallback<Unit>): Cancelable
+    fun leave(reason: String? = null,
+              callback: MatrixCallback<Unit>): Cancelable
 }
diff --git a/vector/src/main/java/im/vector/riotx/features/home/room/detail/RoomDetailViewModel.kt b/vector/src/main/java/im/vector/riotx/features/home/room/detail/RoomDetailViewModel.kt
index abdcc46f6a..00a31db455 100644
--- a/vector/src/main/java/im/vector/riotx/features/home/room/detail/RoomDetailViewModel.kt
+++ b/vector/src/main/java/im/vector/riotx/features/home/room/detail/RoomDetailViewModel.kt
@@ -200,9 +200,10 @@ class RoomDetailViewModel @AssistedInject constructor(@Assisted initialState: Ro
         invisibleEventsObservable.accept(action)
     }
 
-    fun getMember(userId: String) : RoomMember? {
-       return room.getRoomMember(userId)
+    fun getMember(userId: String): RoomMember? {
+        return room.getRoomMember(userId)
     }
+
     /**
      * Convert a send mode to a draft and save the draft
      */
@@ -266,7 +267,7 @@ class RoomDetailViewModel @AssistedInject constructor(@Assisted initialState: Ro
                 }
             }
             session.rx()
-                    .joinRoom(roomId, null, viaServer)
+                    .joinRoom(roomId, viaServers = viaServer)
                     .map { roomId }
                     .execute {
                         copy(tombstoneEventHandling = it)
@@ -557,7 +558,7 @@ class RoomDetailViewModel @AssistedInject constructor(@Assisted initialState: Ro
     }
 
     private fun handleAcceptInvite() {
-        room.join(null, callback = object : MatrixCallback<Unit> {})
+        room.join(callback = object : MatrixCallback<Unit> {})
     }
 
     private fun handleEditAction(action: RoomDetailAction.EnterEditMode) {
diff --git a/vector/src/main/java/im/vector/riotx/features/home/room/list/RoomListViewModel.kt b/vector/src/main/java/im/vector/riotx/features/home/room/list/RoomListViewModel.kt
index 8e9e76099d..a9ea831723 100644
--- a/vector/src/main/java/im/vector/riotx/features/home/room/list/RoomListViewModel.kt
+++ b/vector/src/main/java/im/vector/riotx/features/home/room/list/RoomListViewModel.kt
@@ -123,7 +123,7 @@ class RoomListViewModel @Inject constructor(initialState: RoomListViewState,
             )
         }
 
-        session.getRoom(roomId)?.join(null, emptyList(), object : MatrixCallback<Unit> {
+        session.getRoom(roomId)?.join(callback = object : MatrixCallback<Unit> {
             override fun onSuccess(data: Unit) {
                 // We do not update the joiningRoomsIds here, because, the room is not joined yet regarding the sync data.
                 // Instead, we wait for the room to be joined
diff --git a/vector/src/main/java/im/vector/riotx/features/notifications/NotificationBroadcastReceiver.kt b/vector/src/main/java/im/vector/riotx/features/notifications/NotificationBroadcastReceiver.kt
index 447137d263..c9dc131b42 100644
--- a/vector/src/main/java/im/vector/riotx/features/notifications/NotificationBroadcastReceiver.kt
+++ b/vector/src/main/java/im/vector/riotx/features/notifications/NotificationBroadcastReceiver.kt
@@ -74,14 +74,14 @@ class NotificationBroadcastReceiver : BroadcastReceiver() {
     private fun handleJoinRoom(roomId: String) {
         activeSessionHolder.getSafeActiveSession()?.let { session ->
             session.getRoom(roomId)
-                    ?.join(null, emptyList(), object : MatrixCallback<Unit> {})
+                    ?.join(callback = object : MatrixCallback<Unit> {})
         }
     }
 
     private fun handleRejectRoom(roomId: String) {
         activeSessionHolder.getSafeActiveSession()?.let { session ->
             session.getRoom(roomId)
-                    ?.leave(null, object : MatrixCallback<Unit> {})
+                    ?.leave(callback = object : MatrixCallback<Unit> {})
         }
     }
 
diff --git a/vector/src/main/java/im/vector/riotx/features/roomdirectory/RoomDirectoryViewModel.kt b/vector/src/main/java/im/vector/riotx/features/roomdirectory/RoomDirectoryViewModel.kt
index 3f8b6883ab..d89f0e2b99 100644
--- a/vector/src/main/java/im/vector/riotx/features/roomdirectory/RoomDirectoryViewModel.kt
+++ b/vector/src/main/java/im/vector/riotx/features/roomdirectory/RoomDirectoryViewModel.kt
@@ -214,7 +214,7 @@ class RoomDirectoryViewModel @AssistedInject constructor(@Assisted initialState:
             )
         }
 
-        session.joinRoom(action.roomId, null, emptyList(), object : MatrixCallback<Unit> {
+        session.joinRoom(action.roomId, callback = object : MatrixCallback<Unit> {
             override fun onSuccess(data: Unit) {
                 // We do not update the joiningRoomsIds here, because, the room is not joined yet regarding the sync data.
                 // Instead, we wait for the room to be joined
diff --git a/vector/src/main/java/im/vector/riotx/features/roomdirectory/roompreview/RoomPreviewViewModel.kt b/vector/src/main/java/im/vector/riotx/features/roomdirectory/roompreview/RoomPreviewViewModel.kt
index 42659b2b20..54c86537d2 100644
--- a/vector/src/main/java/im/vector/riotx/features/roomdirectory/roompreview/RoomPreviewViewModel.kt
+++ b/vector/src/main/java/im/vector/riotx/features/roomdirectory/roompreview/RoomPreviewViewModel.kt
@@ -97,7 +97,7 @@ class RoomPreviewViewModel @AssistedInject constructor(@Assisted initialState: R
             )
         }
 
-        session.joinRoom(state.roomId, null, emptyList(), object : MatrixCallback<Unit> {
+        session.joinRoom(state.roomId, callback = object : MatrixCallback<Unit> {
             override fun onSuccess(data: Unit) {
                 // We do not update the joiningRoomsIds here, because, the room is not joined yet regarding the sync data.
                 // Instead, we wait for the room to be joined