Fix lint errors

app/src/main/java/org/tasks/auth/SignInViewModel.kt

@@ -52,7 +52,7 @@ class SignInViewModel @Inject constructor(
         }
 
         ex?.let {
-            error.value = ex
+            error.value = it
             return null
         }
 

app/src/main/java/org/tasks/billing/Inventory.kt

@@ -26,7 +26,7 @@ class Inventory @Inject constructor(
         private val caldavDao: CaldavDao
 ) {
     private val purchases: MutableMap<String, Purchase> = HashMap()
-    val subscription = MutableLiveData<Purchase>()
+    val subscription = MutableLiveData<Purchase?>()
 
     var hasTasksSubscription = false
         private set