Use non nullable parameters, delete unused functions

Signed-off-by: alperozturk <alper_ozturk@proton.me>

app/src/main/java/com/owncloud/android/ui/preview/PreviewImageActivity.java

@@ -166,7 +166,7 @@ public class PreviewImageActivity extends FileActivity implements
 
             if (parentFolder == null) {
                 // should not be necessary
-                parentFolder = getStorageManager().getFileByPath(OCFile.ROOT_PATH);
+                parentFolder = getStorageManager().getFileByEncryptedRemotePath(OCFile.ROOT_PATH);
             }
 
             previewImagePagerAdapter = new PreviewImagePagerAdapter(
@@ -410,9 +410,8 @@ public class PreviewImageActivity extends FileActivity implements
 
         if (currentFile != null) {
             updateActionBarTitle(currentFile.getFileName());
+            setDrawerIndicatorEnabled(false);
         }
-
-        setDrawerIndicatorEnabled(false);
     }
 
     public void updateActionBarTitle(String title) {

app/src/main/java/com/owncloud/android/ui/preview/PreviewImagePagerAdapter.kt

@@ -46,16 +46,15 @@ class PreviewImagePagerAdapter : FragmentStateAdapter {
      */
     @Suppress("LongParameterList")
     constructor(
-        fragmentActivity: FragmentActivity?,
+        fragmentActivity: FragmentActivity,
         selectedFile: OCFile?,
         parentFolder: OCFile?,
         user: User,
-        storageManager: FileDataStorageManager?,
+        storageManager: FileDataStorageManager,
         onlyOnDevice: Boolean,
         preferences: AppPreferences
-    ) : super(fragmentActivity!!) {
+    ) : super(fragmentActivity) {
         requireNotNull(parentFolder) { "NULL parent folder" }
-        requireNotNull(storageManager) { "NULL storage manager" }
 
         this.user = user
         this.selectedFile = selectedFile
@@ -80,14 +79,13 @@ class PreviewImagePagerAdapter : FragmentStateAdapter {
      * @param storageManager  Bridge to database.
      */
     constructor(
-        fragmentActivity: FragmentActivity?,
+        fragmentActivity: FragmentActivity,
         type: VirtualFolderType?,
         user: User,
-        storageManager: FileDataStorageManager?
-    ) : super(fragmentActivity!!) {
+        storageManager: FileDataStorageManager
+    ) : super(fragmentActivity) {
         requireNotNull(type) { "NULL parent folder" }
         require(type != VirtualFolderType.NONE) { "NONE virtual folder type" }
-        requireNotNull(storageManager) { "NULL storage manager" }
 
         this.user = user
         mStorageManager = storageManager
@@ -178,16 +176,6 @@ class PreviewImagePagerAdapter : FragmentStateAdapter {
         return imageFiles.indexOf(file)
     }
 
-    fun getPageTitle(position: Int): CharSequence {
-        val file = getFileAt(position)
-
-        return if (file != null) {
-            file.fileName
-        } else {
-            ""
-        }
-    }
-
     fun updateFile(position: Int, file: OCFile) {
         val fragmentToUpdate = mCachedFragments[position]
         if (fragmentToUpdate != null) {