diff --git a/app/src/main/java/org/kiwix/kiwixmobile/intro/CustomPageIndicator.kt b/app/src/main/java/org/kiwix/kiwixmobile/intro/CustomPageIndicator.kt
index cc5b7baf0..51593b568 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/intro/CustomPageIndicator.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/intro/CustomPageIndicator.kt
@@ -49,6 +49,7 @@ import kotlin.math.min
  * We refactor this java file to kotlin file
  */
 
+@Suppress("UnsafeCallOnNullableType")
 class CustomPageIndicator @JvmOverloads constructor(
   context: Context,
   attrs: AttributeSet? = null,
@@ -114,10 +115,10 @@ class CustomPageIndicator @JvmOverloads constructor(
   fun setViewPager(viewPager: ViewPager) {
     this.viewPager = viewPager
     viewPager.addOnPageChangeListener(this)
-    setPageCount(viewPager.adapter!!.count)
-    viewPager.adapter!!.registerDataSetObserver(object : DataSetObserver() {
+    viewPager.adapter?.count?.let(::setPageCount)
+    viewPager.adapter?.registerDataSetObserver(object : DataSetObserver() {
       override fun onChanged() {
-        setPageCount(this@CustomPageIndicator.viewPager!!.adapter!!.count)
+        this@CustomPageIndicator.viewPager?.adapter?.count?.let(::setPageCount)
       }
     })
     setCurrentPageImmediate()
@@ -560,6 +561,7 @@ class CustomPageIndicator @JvmOverloads constructor(
   /**
    * A [ValueAnimator] that starts once a given predicate returns true.
    */
+  @Suppress("UnnecessaryAbstractClass")
   abstract inner class PendingStartAnimator(private var predicate: StartPredicate) :
     ValueAnimator() {
     private var hasStarted = false
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/language/viewmodel/LanguageViewModel.kt b/app/src/main/java/org/kiwix/kiwixmobile/language/viewmodel/LanguageViewModel.kt
index 40cc8fd96..47fd4caf3 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/language/viewmodel/LanguageViewModel.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/language/viewmodel/LanguageViewModel.kt
@@ -46,7 +46,7 @@ class LanguageViewModel @Inject constructor(
 
   init {
     compositeDisposable.addAll(
-      actions.map { reduce(it, state.value!!) }
+      actions.map { state.value?.let { value -> reduce(it, value) } }
         .distinctUntilChanged()
         .subscribe(state::postValue, Throwable::printStackTrace),
       languageDao.languages().filter { it.isNotEmpty() }
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/localFileTransfer/SenderDevice.kt b/app/src/main/java/org/kiwix/kiwixmobile/localFileTransfer/SenderDevice.kt
index e9458c9d2..085c46d90 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/localFileTransfer/SenderDevice.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/localFileTransfer/SenderDevice.kt
@@ -59,18 +59,21 @@ internal class SenderDevice(
       .forEachIndexed { fileIndex, fileItem ->
         try {
           Socket().use { socket ->
-            context.contentResolver.openInputStream(fileItem?.fileUri!!).use { fileInputStream ->
-              socket.bind(null)
-              socket.connect(
-                InetSocketAddress(hostAddress, WifiDirectManager.FILE_TRANSFER_PORT),
-                TIME_OUT
-              )
-              Log.d(TAG, "Sender socket connected to server - " + socket.isConnected)
-              publishProgress(fileIndex, FileItem.FileStatus.SENDING)
-              val socketOutputStream = socket.getOutputStream()
-              copyToOutputStream(fileInputStream!!, socketOutputStream)
-              if (BuildConfig.DEBUG) Log.d(TAG, "Sender: Data written")
-              publishProgress(fileIndex, FileItem.FileStatus.SENT)
+            fileItem?.fileUri?.let {
+              context.contentResolver.openInputStream(it).use { fileInputStream ->
+                socket.bind(null)
+                socket.connect(
+                  InetSocketAddress(hostAddress, WifiDirectManager.FILE_TRANSFER_PORT),
+                  TIME_OUT
+                )
+                Log.d(TAG, "Sender socket connected to server - " + socket.isConnected)
+                publishProgress(fileIndex, FileItem.FileStatus.SENDING)
+                val socketOutputStream = socket.getOutputStream()
+                @Suppress("UnsafeCallOnNullableType")
+                copyToOutputStream(fileInputStream!!, socketOutputStream)
+                if (BuildConfig.DEBUG) Log.d(TAG, "Sender: Data written")
+                publishProgress(fileIndex, FileItem.FileStatus.SENT)
+              }
             }
           }
         } catch (e: IOException) {
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/library/OnlineLibraryFragment.kt b/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/library/OnlineLibraryFragment.kt
index da42d3182..086423547 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/library/OnlineLibraryFragment.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/library/OnlineLibraryFragment.kt
@@ -278,7 +278,7 @@ class OnlineLibraryFragment : BaseFragment(), FragmentActivityExtensions {
   }
 
   private fun onRefreshStateChange(isRefreshing: Boolean?) {
-    fragmentDestinationDownloadBinding?.librarySwipeRefresh?.isRefreshing = isRefreshing!!
+    fragmentDestinationDownloadBinding?.librarySwipeRefresh?.isRefreshing = isRefreshing == true
   }
 
   private fun onNetworkStateChange(networkState: NetworkState?) {
@@ -325,8 +325,10 @@ class OnlineLibraryFragment : BaseFragment(), FragmentActivityExtensions {
   }
 
   private fun onLibraryItemsChange(it: List<LibraryListItem>?) {
-    libraryAdapter.items = it!!
-    if (it.isEmpty()) {
+    if (it != null) {
+      libraryAdapter.items = it
+    }
+    if (it?.isEmpty() == true) {
       fragmentDestinationDownloadBinding?.libraryErrorText?.setText(
         if (isNotConnected) R.string.no_network_connection
         else R.string.no_items_msg
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/reader/KiwixReaderFragment.kt b/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/reader/KiwixReaderFragment.kt
index 4e242cc6c..b879a85e2 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/reader/KiwixReaderFragment.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/nav/destination/reader/KiwixReaderFragment.kt
@@ -262,6 +262,7 @@ class KiwixReaderFragment : CoreReaderFragment() {
     restoreTabs(zimArticles, zimPositions, currentTab)
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   override fun createWebView(attrs: AttributeSet?): ToolbarScrollingKiwixWebView {
     return ToolbarScrollingKiwixWebView(
       requireContext(), this, attrs!!, activityMainRoot as ViewGroup, videoView!!,
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/settings/KiwixPrefsFragment.kt b/app/src/main/java/org/kiwix/kiwixmobile/settings/KiwixPrefsFragment.kt
index a5791e4de..8eafc7d6c 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/settings/KiwixPrefsFragment.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/settings/KiwixPrefsFragment.kt
@@ -68,11 +68,11 @@ class KiwixPrefsFragment : CorePrefsFragment() {
       showPermissionPreference()
       val externalStorageManager = Environment.isExternalStorageManager()
       if (externalStorageManager) {
-        permissionPref!!.setSummary(org.kiwix.kiwixmobile.core.R.string.allowed)
+        permissionPref?.setSummary(org.kiwix.kiwixmobile.core.R.string.allowed)
       } else {
-        permissionPref!!.setSummary(org.kiwix.kiwixmobile.core.R.string.not_allowed)
+        permissionPref?.setSummary(org.kiwix.kiwixmobile.core.R.string.not_allowed)
       }
-      permissionPref.onPreferenceClickListener =
+      permissionPref?.onPreferenceClickListener =
         Preference.OnPreferenceClickListener {
           activity?.let(FragmentActivity::navigateToSettings)
           true
@@ -84,7 +84,7 @@ class KiwixPrefsFragment : CorePrefsFragment() {
     val preferenceCategory = findPreference<PreferenceCategory>(
       PREF_PERMISSION
     )
-    preferenceCategory!!.isVisible = true
+    preferenceCategory?.isVisible = true
   }
 
   companion object {
diff --git a/app/src/main/java/org/kiwix/kiwixmobile/zimManager/ZimManageViewModel.kt b/app/src/main/java/org/kiwix/kiwixmobile/zimManager/ZimManageViewModel.kt
index d41d7eff1..d449f2f25 100644
--- a/app/src/main/java/org/kiwix/kiwixmobile/zimManager/ZimManageViewModel.kt
+++ b/app/src/main/java/org/kiwix/kiwixmobile/zimManager/ZimManageViewModel.kt
@@ -358,6 +358,7 @@ class ZimManageViewModel @Inject constructor(
     locale: Locale
   ) = allLanguages.firstOrNull { it.languageCode == locale.isO3Language }?.active == true
 
+  @Suppress("UnsafeCallOnNullableType")
   private fun combineLibrarySources(
     booksOnFileSystem: List<BookOnDisk>,
     activeDownloads: List<DownloadModel>,
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/CoreApp.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/CoreApp.kt
index e106fc0ec..f3d5d2fa2 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/CoreApp.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/CoreApp.kt
@@ -32,6 +32,7 @@ import org.kiwix.kiwixmobile.core.downloader.DownloadMonitor
 import org.kiwix.kiwixmobile.core.utils.files.FileLogger
 import javax.inject.Inject
 
+@Suppress("UnnecessaryAbstractClass")
 abstract class CoreApp : Application() {
   companion object {
     @JvmStatic
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/base/BasePresenter.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/base/BasePresenter.kt
index b3e546921..bb82216ae 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/base/BasePresenter.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/base/BasePresenter.kt
@@ -24,6 +24,7 @@ import org.kiwix.kiwixmobile.core.base.BaseContract.View
 /**
  * All presenters should inherit from this presenter.
  */
+@Suppress("UnnecessaryAbstractClass")
 abstract class BasePresenter<T : View<*>?> : Presenter<T> {
   @JvmField val compositeDisposable = CompositeDisposable()
   @JvmField var view: T? = null
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/base/adapter/AdapterDelegateManager.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/base/adapter/AdapterDelegateManager.kt
index 5fa5a005a..82a657fa4 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/base/adapter/AdapterDelegateManager.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/base/adapter/AdapterDelegateManager.kt
@@ -27,6 +27,7 @@ class AdapterDelegateManager<T> {
     delegates.put(delegates.size(), delegate)
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   fun createViewHolder(
     parent: ViewGroup,
     viewType: Int
@@ -36,7 +37,7 @@ class AdapterDelegateManager<T> {
     libraryListItem: T,
     holder: RecyclerView.ViewHolder
   ) {
-    delegates[holder.itemViewType]!!.bind(holder, libraryListItem)
+    delegates[holder.itemViewType]?.bind(holder, libraryListItem)
   }
 
   fun getViewTypeFor(item: T) = delegates.keyAt(getDelegateIndexFor(item))
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/dao/NewBookDao.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/dao/NewBookDao.kt
index 8e15a303a..b01e22ee3 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/dao/NewBookDao.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/dao/NewBookDao.kt
@@ -75,6 +75,7 @@ class NewBookDao @Inject constructor(private val box: Box<BookOnDiskEntity>) {
     box.remove(databaseId)
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   fun migrationInsert(books: List<Book>) {
     insert(books.map { BookOnDisk(book = it, file = it.file!!) })
   }
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/di/modules/DatabaseModule.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/di/modules/DatabaseModule.kt
index 8f9b957a1..7de1934d4 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/di/modules/DatabaseModule.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/di/modules/DatabaseModule.kt
@@ -39,6 +39,7 @@ open class DatabaseModule {
     var boxStore: BoxStore? = null
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   // NOT RECOMMENDED TODO use custom runner to load TestApplication
   @Provides @Singleton fun providesBoxStore(context: Context): BoxStore {
     if (boxStore == null) {
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/downloader/DownloaderImpl.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/downloader/DownloaderImpl.kt
index e272ca6d9..52dc10e27 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/downloader/DownloaderImpl.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/downloader/DownloaderImpl.kt
@@ -44,6 +44,7 @@ class DownloaderImpl @Inject constructor(
       )
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   private fun urlProvider(book: Book): Observable<String> =
     if (book.url?.endsWith("meta4") == true) kiwixService.getMetaLinks(book.url!!)
       .map { it.relevantUrl.value }
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/error/ErrorActivity.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/error/ErrorActivity.kt
index bfa88d3ea..ef888d9e9 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/error/ErrorActivity.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/error/ErrorActivity.kt
@@ -63,7 +63,7 @@ open class ErrorActivity : BaseActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     activityKiwixErrorBinding = ActivityKiwixErrorBinding.inflate(layoutInflater)
-    setContentView(activityKiwixErrorBinding!!.root)
+    setContentView(activityKiwixErrorBinding?.root)
     val extras = intent.extras
     exception = if (extras != null && safeContains(extras)) {
       if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
@@ -134,7 +134,7 @@ open class ErrorActivity : BaseActivity() {
   private fun exceptionDetails(): String =
     """
     Exception Details:
-    ${toStackTraceString(exception!!)}
+    ${exception?.let(::toStackTraceString)}
     """.trimIndent()
 
   private fun zimFiles(): String {
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/help/HelpFragment.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/help/HelpFragment.kt
index 6a04a5104..3db5702af 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/help/HelpFragment.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/help/HelpFragment.kt
@@ -40,6 +40,7 @@ import org.kiwix.kiwixmobile.core.main.CoreMainActivity
 import org.kiwix.kiwixmobile.core.utils.CONTACT_EMAIL_ADDRESS
 import org.kiwix.kiwixmobile.core.utils.LanguageUtils.Companion.getCurrentLocale
 
+@Suppress("UnnecessaryAbstractClass")
 abstract class HelpFragment : BaseFragment() {
   private var fragmentHelpBinding: FragmentHelpBinding? = null
   protected open fun rawTitleDescriptionMap(): List<Pair<Int, Int>> = emptyList()
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/main/CoreReaderFragment.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/main/CoreReaderFragment.kt
index 2c6f2427f..409289a75 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/main/CoreReaderFragment.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/main/CoreReaderFragment.kt
@@ -610,16 +610,18 @@ abstract class CoreReaderFragment :
   }
 
   private fun setupTabsAdapter() {
-    tabsAdapter = TabsAdapter(
-      requireActivity() as AppCompatActivity,
-      webViewList,
-      painter!!
-    ).apply {
-      registerAdapterDataObserver(object : AdapterDataObserver() {
-        override fun onChanged() {
-          mainMenu?.updateTabIcon(itemCount)
-        }
-      })
+    tabsAdapter = painter?.let {
+      TabsAdapter(
+        requireActivity() as AppCompatActivity,
+        webViewList,
+        it
+      ).apply {
+        registerAdapterDataObserver(object : AdapterDataObserver() {
+          override fun onChanged() {
+            mainMenu?.updateTabIcon(itemCount)
+          }
+        })
+      }
     }
   }
 
@@ -638,7 +640,7 @@ abstract class CoreReaderFragment :
       override fun onSectionClick(view: View?, position: Int) {
         loadUrlWithCurrentWebview(
           "javascript:document.getElementById('" +
-            documentSections!![position].id.replace("'", "\\'") +
+            documentSections?.get(position)?.id?.replace("'", "\\'") +
             "').scrollIntoView();"
         )
         drawerLayout?.closeDrawers()
@@ -670,7 +672,7 @@ abstract class CoreReaderFragment :
         if (tabsAdapter.selected < webViewList.size &&
           recyclerView.layoutManager != null
         ) {
-          recyclerView.layoutManager!!.scrollToPosition(tabsAdapter.selected)
+          recyclerView.layoutManager?.scrollToPosition(tabsAdapter.selected)
         }
       }
       // Notify the tabs adapter to update the UI when the tab switcher is shown
@@ -886,7 +888,8 @@ abstract class CoreReaderFragment :
   }
 
   private fun getValidTitle(zimFileTitle: String?): String =
-    if (isAdded && isInvalidTitle(zimFileTitle)) getString(R.string.app_name) else zimFileTitle!!
+    if (isAdded && isInvalidTitle(zimFileTitle)) getString(R.string.app_name)
+    else zimFileTitle.toString()
 
   private fun isInvalidTitle(zimFileTitle: String?): Boolean =
     zimFileTitle == null || zimFileTitle.trim { it <= ' ' }.isEmpty()
@@ -1058,6 +1061,7 @@ abstract class CoreReaderFragment :
     return null
   }
 
+  @Suppress("UnsafeCallOnNullableType")
   protected open fun createWebView(attrs: AttributeSet?): ToolbarScrollingKiwixWebView? {
     return if (activityMainRoot != null) {
       ToolbarScrollingKiwixWebView(
@@ -1739,10 +1743,10 @@ abstract class CoreReaderFragment :
   }
 
   private fun searchForTitle(title: String?, openInNewTab: Boolean) {
-    val articleUrl: String? = if (title!!.startsWith("A/")) {
+    val articleUrl: String? = if (title?.startsWith("A/") == true) {
       title
     } else {
-      zimReaderContainer?.getPageUrlFromTitle(title)
+      title?.let { zimReaderContainer?.getPageUrlFromTitle(it) }
     }
     if (openInNewTab) {
       openArticleInNewTab(articleUrl)
@@ -1764,14 +1768,16 @@ abstract class CoreReaderFragment :
   }
 
   protected open fun createMainMenu(menu: Menu?): MainMenu? =
-    menuFactory?.create(
-      menu!!,
-      webViewList,
-      urlIsValid(),
-      menuClickListener = this,
-      disableReadAloud = false,
-      disableTabs = false
-    )
+    menu?.let {
+      menuFactory?.create(
+        it,
+        webViewList,
+        urlIsValid(),
+        menuClickListener = this,
+        disableReadAloud = false,
+        disableTabs = false
+      )
+    }
 
   protected fun urlIsValid(): Boolean = getCurrentWebView()?.url != null
 
@@ -1851,6 +1857,7 @@ abstract class CoreReaderFragment :
             requireActivity()
           )
         )
+        @Suppress("UnsafeCallOnNullableType")
         getCurrentWebView()?.let {
           val history = HistoryItem(
             it.url!!,
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/page/viewmodel/PageViewModel.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/page/viewmodel/PageViewModel.kt
index edda2f164..7dbfbc817 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/page/viewmodel/PageViewModel.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/page/viewmodel/PageViewModel.kt
@@ -66,7 +66,7 @@ abstract class PageViewModel<T : Page, S : PageState<T>>(
   }
 
   private fun viewStateReducer(): Disposable =
-    actions.map { reduce(it, state.value!!) }
+    actions.map { state.value?.let { value -> reduce(it, value) } }
       .subscribe(state::postValue, Throwable::printStackTrace)
 
   protected fun addDisposablesToCompositeDisposable() {
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/utils/dialog/RateDialogHandler.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/utils/dialog/RateDialogHandler.kt
index c6d907199..16129357c 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/utils/dialog/RateDialogHandler.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/utils/dialog/RateDialogHandler.kt
@@ -60,7 +60,7 @@ class RateDialogHandler @Inject constructor(
   fun checkForRateDialog(@IdRes iconResId: Int) {
     isFirstRun = sharedPreferenceUtil.prefIsFirstRun
     visitCounterPref = RateAppCounter(activity)
-    tempVisitCount = visitCounterPref?.count!!
+    tempVisitCount = visitCounterPref?.count ?: 0
     ++tempVisitCount
     visitCounterPref?.count = tempVisitCount
     if (shouldShowRateDialog() && NetworkUtils.isNetworkAvailable(activity)) {
diff --git a/core/src/main/java/org/kiwix/kiwixmobile/core/utils/files/FileUtils.kt b/core/src/main/java/org/kiwix/kiwixmobile/core/utils/files/FileUtils.kt
index 9fcf1f422..8848cde82 100644
--- a/core/src/main/java/org/kiwix/kiwixmobile/core/utils/files/FileUtils.kt
+++ b/core/src/main/java/org/kiwix/kiwixmobile/core/utils/files/FileUtils.kt
@@ -136,9 +136,9 @@ object FileUtils {
           null
         }
     } else if (uri.scheme != null) {
-      if ("content".equals(uri.scheme!!, ignoreCase = true)) {
+      if ("content".equals(uri.scheme, ignoreCase = true)) {
         return contentQuery(context, uri)
-      } else if ("file".equals(uri.scheme!!, ignoreCase = true)) {
+      } else if ("file".equals(uri.scheme, ignoreCase = true)) {
         return uri.path
       }
     } else {
diff --git a/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadFragment.kt b/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadFragment.kt
index 07562c3a3..c72e240c7 100644
--- a/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadFragment.kt
+++ b/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadFragment.kt
@@ -100,25 +100,28 @@ class CustomDownloadFragment : BaseFragment(), FragmentActivityExtensions {
     activity?.finish()
   }
 
-  private fun render(state: State) {
+  private fun render(state: State): Unit? {
     return when (state) {
       DownloadRequired ->
         fragmentCustomDownloadBinding?.cdViewAnimator?.setDistinctDisplayedChild(0)
+
       is DownloadInProgress -> {
         fragmentCustomDownloadBinding?.cdViewAnimator?.setDistinctDisplayedChild(1)
-        render(state.downloads[0])
+        showDownloadingProgress(state.downloads[0])
       }
+
       is DownloadFailed -> {
         fragmentCustomDownloadBinding?.cdViewAnimator?.setDistinctDisplayedChild(2)
         fragmentCustomDownloadBinding?.customDownloadError?.cdErrorText?.text =
           context?.let(state.downloadState::toReadableState)
       }
+
       DownloadComplete ->
         fragmentCustomDownloadBinding?.cdViewAnimator?.setDistinctDisplayedChild(3)
-    }!!
+    }
   }
 
-  private fun render(downloadItem: DownloadItem) {
+  private fun showDownloadingProgress(downloadItem: DownloadItem) {
     fragmentCustomDownloadBinding?.customDownloadInProgress?.apply {
       cdDownloadState.text = downloadItem.readableEta
       cdEta.text = context?.let(downloadItem.downloadState::toReadableState)
diff --git a/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadViewModel.kt b/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadViewModel.kt
index 5920ec6bc..3aa363179 100644
--- a/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadViewModel.kt
+++ b/custom/src/main/java/org/kiwix/kiwixmobile/custom/download/CustomDownloadViewModel.kt
@@ -59,7 +59,9 @@ class CustomDownloadViewModel @Inject constructor(
     )
   }
 
-  private fun reducer() = actions.map { reduce(it, state.value!!) }
+  private fun reducer() = actions.map {
+    state.value?.let { value -> reduce(it, value) }
+  }
     .distinctUntilChanged()
     .subscribe(state::postValue, Throwable::printStackTrace)
 
diff --git a/custom/src/main/java/org/kiwix/kiwixmobile/custom/main/CustomReaderFragment.kt b/custom/src/main/java/org/kiwix/kiwixmobile/custom/main/CustomReaderFragment.kt
index 15c3b33d8..f4bf65507 100644
--- a/custom/src/main/java/org/kiwix/kiwixmobile/custom/main/CustomReaderFragment.kt
+++ b/custom/src/main/java/org/kiwix/kiwixmobile/custom/main/CustomReaderFragment.kt
@@ -76,7 +76,7 @@ class CustomReaderFragment : CoreReaderFragment() {
         toolbarToc?.isEnabled = false
       }
       with(activity as AppCompatActivity) {
-        supportActionBar!!.setDisplayHomeAsUpEnabled(true)
+        supportActionBar?.setDisplayHomeAsUpEnabled(true)
         toolbar?.let { setupDrawerToggle(it) }
       }
       loadPageFromNavigationArguments()
@@ -187,14 +187,16 @@ class CustomReaderFragment : CoreReaderFragment() {
   }
 
   override fun createMainMenu(menu: Menu?): MainMenu? {
-    return menuFactory?.create(
-      menu!!,
-      webViewList,
-      urlIsValid(),
-      this,
-      BuildConfig.DISABLE_READ_ALOUD,
-      BuildConfig.DISABLE_TABS
-    )
+    return menu?.let {
+      menuFactory?.create(
+        it,
+        webViewList,
+        urlIsValid(),
+        this,
+        BuildConfig.DISABLE_READ_ALOUD,
+        BuildConfig.DISABLE_TABS
+      )
+    }
   }
 
   override fun showOpenInNewTabDialog(url: String) {