Fall back to internal cache if external is null

app/src/main/java/org/tasks/preferences/Preferences.java

@@ -426,10 +426,15 @@ public class Preferences {
   }
 
   public Uri getCacheDirectory() {
+    File cacheDir = context.getExternalCacheDir();
+    if (cacheDir == null) {
+      cacheDir = context.getCacheDir();
+    }
+
     if (atLeastKitKat()) {
-      return DocumentFile.fromFile(context.getExternalCacheDir()).getUri();
+      return DocumentFile.fromFile(cacheDir).getUri();
     } else {
-      return Uri.fromFile(context.getExternalCacheDir());
+      return Uri.fromFile(cacheDir);
     }
   }
 

app/src/main/res/xml/file_provider_paths.xml

@@ -6,4 +6,7 @@
     <external-cache-path
         name="external_cache"
         path="." />
+    <cache-path
+      name="internal_cache"
+      path="." />
 </paths>