diff --git a/app/src/main/java/pl/szczodrzynski/edziennik/data/api/edziennik/mobidziennik/data/web/MobidziennikWebAttendance.kt b/app/src/main/java/pl/szczodrzynski/edziennik/data/api/edziennik/mobidziennik/data/web/MobidziennikWebAttendance.kt
index f23478b6..cbd797b1 100644
--- a/app/src/main/java/pl/szczodrzynski/edziennik/data/api/edziennik/mobidziennik/data/web/MobidziennikWebAttendance.kt
+++ b/app/src/main/java/pl/szczodrzynski/edziennik/data/api/edziennik/mobidziennik/data/web/MobidziennikWebAttendance.kt
@@ -48,7 +48,7 @@ class MobidziennikWebAttendance(override val data: DataMobidziennik,
         //syncWeeks.clear()
         //syncWeeks += Date.fromY_m_d("2019-12-19")
 
-        syncWeeks.minBy { it.value }?.let {
+        syncWeeks.minByOrNull { it.value }?.let {
             data.toRemove.add(DataRemoveModel.Attendance.from(it))
         }
 
diff --git a/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/login/LoginProgressFragment.kt b/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/login/LoginProgressFragment.kt
index 7550b08c..aaebbac0 100644
--- a/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/login/LoginProgressFragment.kt
+++ b/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/login/LoginProgressFragment.kt
@@ -76,7 +76,7 @@ class LoginProgressFragment : Fragment(), CoroutineScope {
 
             val maxProfileId = max(
                     app.db.profileDao().lastId ?: 0,
-                    activity.profiles.maxBy { it.profile.id }?.profile?.id ?: 0
+                    activity.profiles.maxByOrNull { it.profile.id }?.profile?.id ?: 0
             )
             val loginType = args.getInt("loginType", -1)
             val loginMode = args.getInt("loginMode", 0)
diff --git a/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/timetable/TimetableFragment.kt b/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/timetable/TimetableFragment.kt
index 970daeec..85332fe1 100644
--- a/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/timetable/TimetableFragment.kt
+++ b/app/src/main/java/pl/szczodrzynski/edziennik/ui/modules/timetable/TimetableFragment.kt
@@ -120,8 +120,8 @@ class TimetableFragment : Fragment(), CoroutineScope {
             }
 
             val lessonRanges = app.db.lessonRangeDao().getAllNow(App.profileId)
-            startHour = lessonRanges.map { it.startTime.hour }.min() ?: DEFAULT_START_HOUR
-            endHour = lessonRanges.map { it.endTime.hour }.max()?.plus(1) ?: DEFAULT_END_HOUR
+            startHour = lessonRanges.map { it.startTime.hour }.minOrNull() ?: DEFAULT_START_HOUR
+            endHour = lessonRanges.map { it.endTime.hour }.maxOrNull()?.plus(1) ?: DEFAULT_END_HOUR
         }
         deferred.await()
         if (!isAdded)
diff --git a/build.gradle b/build.gradle
index 9214ceda..ac506325 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,7 +2,7 @@
 
 buildscript {
     ext {
-        kotlin_version = '1.4.31'
+        kotlin_version = '1.5.20'
 
         release = [
                 versionName: "4.8.2",