Fix crash on null parameter

app/src/main/java/com/todoroo/astrid/gtasks/auth/GtasksLoginActivity.kt

@@ -92,7 +92,7 @@ class GtasksLoginActivity : InjectingAppCompatActivity() {
                         }
                     }
 
-                    override fun authenticationFailed(message: String) {
+                    override fun authenticationFailed(message: String?) {
                         setResult(Activity.RESULT_CANCELED, Intent().putExtra(EXTRA_ERROR, message))
                         DialogUtilities.dismissDialog(this@GtasksLoginActivity, pd)
                         finish()

app/src/main/java/org/tasks/play/AuthResultHandler.java

@@ -1,7 +0,0 @@
-package org.tasks.play;
-
-public interface AuthResultHandler {
-  void authenticationSuccessful(String accountName);
-
-  void authenticationFailed(String message);
-}

app/src/main/java/org/tasks/play/AuthResultHandler.kt

@@ -0,0 +1,7 @@
+package org.tasks.play
+
+interface AuthResultHandler {
+    fun authenticationSuccessful(accountName: String)
+
+    fun authenticationFailed(message: String?)
+}