Handle null DocumentFile name

app/src/main/java/com/todoroo/astrid/backup/BackupConstants.kt

@@ -43,7 +43,7 @@ object BackupConstants {
 
     private val MATCHER = Pattern.compile("(auto|user)\\.(\\d{2})(\\d{2})(\\d{2})-(\\d{2})(\\d{2})\\.json")
 
-    fun isBackupFile(name: String) = MATCHER.matcher(name).matches()
+    fun isBackupFile(name: String?) = name?.let { MATCHER.matcher(it).matches() } ?: false
 
     fun getTimestamp(file: java.io.File): Long {
         return getTimestampFromFilename(file.name) ?: file.lastModified()

app/src/main/java/org/tasks/preferences/PreferencesViewModel.kt

@@ -84,7 +84,7 @@ class PreferencesViewModel @ViewModelInject constructor(
                 ContentResolver.SCHEME_CONTENT -> {
                     DocumentFile.fromTreeUri(context, uri)
                             ?.listFiles()
-                            ?.filter { BackupConstants.isBackupFile(it.name!!) }
+                            ?.filter { BackupConstants.isBackupFile(it.name) }
                             ?.map { BackupConstants.getTimestamp(it) }
                 }
                 ContentResolver.SCHEME_FILE -> {