diff --git a/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.java b/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.java
deleted file mode 100644
index 0219c10cf..000000000
--- a/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.java
+++ /dev/null
@@ -1,41 +0,0 @@
-package fr.free.nrw.commons.upload;
-
-import android.os.Bundle;
-import androidx.annotation.Nullable;
-import fr.free.nrw.commons.di.CommonsDaggerSupportFragment;
-
-/**
- * The base fragment of the fragments in upload
- */
-public class UploadBaseFragment extends CommonsDaggerSupportFragment  {
-
-    public Callback callback;
-    public static final String CALLBACK = "callback";
-
-    @Override
-    public void onCreate(@Nullable Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-    }
-
-    public void setCallback(Callback callback) {
-        this.callback = callback;
-    }
-
-    protected void onBecameVisible() {
-    }
-
-    public interface Callback {
-
-        void onNextButtonClicked(int index);
-
-        void onPreviousButtonClicked(int index);
-
-        void showProgress(boolean shouldShow);
-
-        int getIndexInViewFlipper(UploadBaseFragment fragment);
-
-        int getTotalNumberOfSteps();
-
-        boolean isWLMUpload();
-    }
-}
diff --git a/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.kt b/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.kt
new file mode 100644
index 000000000..0cb47273e
--- /dev/null
+++ b/app/src/main/java/fr/free/nrw/commons/upload/UploadBaseFragment.kt
@@ -0,0 +1,26 @@
+package fr.free.nrw.commons.upload
+
+import fr.free.nrw.commons.di.CommonsDaggerSupportFragment
+
+/**
+ * The base fragment of the fragments in upload
+ */
+abstract class UploadBaseFragment : CommonsDaggerSupportFragment() {
+    lateinit var callback: Callback
+
+    protected open fun onBecameVisible() = Unit
+
+    interface Callback {
+        val totalNumberOfSteps: Int
+        val isWLMUpload: Boolean
+
+        fun onNextButtonClicked(index: Int)
+        fun onPreviousButtonClicked(index: Int)
+        fun showProgress(shouldShow: Boolean)
+        fun getIndexInViewFlipper(fragment: UploadBaseFragment?): Int
+    }
+
+    companion object {
+        const val CALLBACK: String = "callback"
+    }
+}
diff --git a/app/src/main/java/fr/free/nrw/commons/upload/categories/UploadCategoriesFragment.kt b/app/src/main/java/fr/free/nrw/commons/upload/categories/UploadCategoriesFragment.kt
index 845f0548f..efec29642 100644
--- a/app/src/main/java/fr/free/nrw/commons/upload/categories/UploadCategoriesFragment.kt
+++ b/app/src/main/java/fr/free/nrw/commons/upload/categories/UploadCategoriesFragment.kt
@@ -220,7 +220,7 @@ class UploadCategoriesFragment : UploadBaseFragment(), CategoriesContract.View {
     }
 
     override fun goToNextScreen() {
-        callback?.onNextButtonClicked(callback.getIndexInViewFlipper(this))
+        callback.onNextButtonClicked(callback.getIndexInViewFlipper(this))
     }
 
     override fun showNoCategorySelected() {
@@ -322,7 +322,7 @@ class UploadCategoriesFragment : UploadBaseFragment(), CategoriesContract.View {
             mediaDetailFragment.onResume()
             goBackToPreviousScreen()
         } else {
-            callback?.onPreviousButtonClicked(callback.getIndexInViewFlipper(this))
+            callback.onPreviousButtonClicked(callback.getIndexInViewFlipper(this))
         }
     }
 
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/upload/categories/UploadCategoriesFragmentUnitTests.kt b/app/src/test/kotlin/fr/free/nrw/commons/upload/categories/UploadCategoriesFragmentUnitTests.kt
index f2d54132c..75d6b8a4f 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/upload/categories/UploadCategoriesFragmentUnitTests.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/upload/categories/UploadCategoriesFragmentUnitTests.kt
@@ -62,6 +62,7 @@ class UploadCategoriesFragmentUnitTests {
         OkHttpConnectionFactory.CLIENT = createTestClient()
         val activity = Robolectric.buildActivity(UploadActivity::class.java).create().get()
         fragment = UploadCategoriesFragment()
+        fragment.callback = callback
         fragmentManager = activity.supportFragmentManager
         val fragmentTransaction: FragmentTransaction = fragmentManager.beginTransaction()
         fragmentTransaction.add(fragment, null)