diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/MXOlmDevice.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/MXOlmDevice.kt
index d9387ad3..7c5131fc 100755
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/MXOlmDevice.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/MXOlmDevice.kt
@@ -79,8 +79,7 @@ internal class MXOlmDevice @Inject constructor(
     //
     // The first level keys are timeline ids.
     // The second level keys are strings of form "<senderKey>|<session_id>|<message_index>"
-    // Values are true.
-    private val inboundGroupSessionMessageIndexes: MutableMap<String, MutableMap<String, Boolean>> = HashMap()
+    private val inboundGroupSessionMessageIndexes: MutableMap<String, MutableSet<String>> = HashMap()
 
     init {
         // Retrieve the account from the store
@@ -662,19 +661,17 @@ internal class MXOlmDevice @Inject constructor(
             }
 
             if (null != timeline) {
-                if (!inboundGroupSessionMessageIndexes.containsKey(timeline)) {
-                    inboundGroupSessionMessageIndexes[timeline] = HashMap()
-                }
+                val timelineSet = inboundGroupSessionMessageIndexes.getOrPut(timeline) { mutableSetOf() }
 
                 val messageIndexKey = senderKey + "|" + sessionId + "|" + decryptResult.mIndex
 
-                if (inboundGroupSessionMessageIndexes[timeline]?.get(messageIndexKey) != null) {
+                if (timelineSet.contains(messageIndexKey)) {
                     val reason = String.format(MXCryptoError.DUPLICATE_MESSAGE_INDEX_REASON, decryptResult.mIndex)
                     Timber.e("## decryptGroupMessage() : $reason")
                     throw MXCryptoError.Base(MXCryptoError.ErrorType.DUPLICATED_MESSAGE_INDEX, reason)
                 }
 
-                inboundGroupSessionMessageIndexes[timeline]!!.put(messageIndexKey, true)
+                timelineSet.add(messageIndexKey)
             }
 
             store.storeInboundGroupSessions(listOf(session))
diff --git a/vector/src/main/java/im/vector/riotx/core/intent/Filename.kt b/vector/src/main/java/im/vector/riotx/core/intent/Filename.kt
index 2b8421f6..3ea25294 100644
--- a/vector/src/main/java/im/vector/riotx/core/intent/Filename.kt
+++ b/vector/src/main/java/im/vector/riotx/core/intent/Filename.kt
@@ -35,9 +35,9 @@ fun getFilenameFromUri(context: Context?, uri: Uri): String? {
     }
     if (result == null) {
         result = uri.path
-        val cut = result.lastIndexOf('/')
+        val cut = result?.lastIndexOf('/') ?: -1
         if (cut != -1) {
-            result = result.substring(cut + 1)
+            result = result?.substring(cut + 1)
         }
     }
     return result
diff --git a/vector/src/main/java/im/vector/riotx/features/crypto/verification/SasVerificationViewModel.kt b/vector/src/main/java/im/vector/riotx/features/crypto/verification/SasVerificationViewModel.kt
index 87a420d3..41c08e68 100644
--- a/vector/src/main/java/im/vector/riotx/features/crypto/verification/SasVerificationViewModel.kt
+++ b/vector/src/main/java/im/vector/riotx/features/crypto/verification/SasVerificationViewModel.kt
@@ -29,7 +29,7 @@ import javax.inject.Inject
 
 
 class SasVerificationViewModel @Inject constructor() : ViewModel(),
-                                                       SasVerificationService.SasVerificationListener {
+        SasVerificationService.SasVerificationListener {
 
 
     companion object {
@@ -40,7 +40,7 @@ class SasVerificationViewModel @Inject constructor() : ViewModel(),
         const val NAVIGATE_CANCELLED = "NAVIGATE_CANCELLED"
     }
 
-    lateinit var sasVerificationService: SasVerificationService
+    private lateinit var sasVerificationService: SasVerificationService
 
     var otherUserId: String? = null
     var otherDeviceId: String? = null
@@ -154,8 +154,8 @@ class SasVerificationViewModel @Inject constructor() : ViewModel(),
 
     override fun onCleared() {
         super.onCleared()
-        sasVerificationService.removeListener(this)
+        if (::sasVerificationService.isInitialized) {
+            sasVerificationService.removeListener(this)
+        }
     }
-
-
 }
\ No newline at end of file