diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/MatrixPatterns.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/MatrixPatterns.kt
index e30d139cd3..bba925b89f 100644
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/MatrixPatterns.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/api/MatrixPatterns.kt
@@ -122,9 +122,9 @@ object MatrixPatterns {
      */
     fun isEventId(str: String?): Boolean {
         return str != null
-               && (str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER
-                   || str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER_V3
-                   || str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER_V4)
+                && (str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER
+                || str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER_V3
+                || str matches PATTERN_CONTAIN_MATRIX_EVENT_IDENTIFIER_V4)
     }
 
     /**
@@ -144,14 +144,6 @@ object MatrixPatterns {
      * @return null if not found or if matrixId is null
      */
     fun extractServerNameFromId(matrixId: String?): String? {
-        if (matrixId == null) {
-            return null
-        }
-
-        val index = matrixId.indexOf(":")
-
-        return if (index == -1) {
-            null
-        } else matrixId.substring(index + 1)
+        return matrixId?.substringAfter(":", missingDelimiterValue = "")?.takeIf { it.isNotEmpty() }
     }
 }
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 1eccba7fa9..15f7bc0694 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
@@ -297,15 +297,11 @@ class RoomDetailViewModel @AssistedInject constructor(@Assisted initialState: Ro
         if (isRoomJoined) {
             setState { copy(tombstoneEventHandling = Success(roomId)) }
         } else {
-            val viaServer = MatrixPatterns.extractServerNameFromId(action.event.senderId).let {
-                if (it.isNullOrBlank()) {
-                    emptyList()
-                } else {
-                    listOf(it)
-                }
-            }
+            val viaServers = MatrixPatterns.extractServerNameFromId(action.event.senderId)
+                    ?.let { listOf(it) }
+                    .orEmpty()
             session.rx()
-                    .joinRoom(roomId, viaServers = viaServer)
+                    .joinRoom(roomId, viaServers = viaServers)
                     .map { roomId }
                     .execute {
                         copy(tombstoneEventHandling = it)