Disallow null response of SuccessCallback

app/src/main/java/com/github/gotify/MissedMessageUtil.kt

@@ -10,10 +10,10 @@ import com.github.gotify.client.model.PagedMessages
 import com.github.gotify.log.Log
 
 internal class MissedMessageUtil(private val api: MessageApi) {
-    fun lastReceivedMessage(successCallback: SuccessCallback<Long?>) {
+    fun lastReceivedMessage(successCallback: SuccessCallback<Long>) {
         api.getMessages(1, 0L).enqueue(
-            Callback.call({ messages: PagedMessages? ->
-                if (messages!!.messages.size == 1) {
+            Callback.call({ messages: PagedMessages ->
+                if (messages.messages.size == 1) {
                     successCallback.onSuccess(messages.messages[0].id)
                 } else {
                     successCallback.onSuccess(NO_MESSAGES)

app/src/main/java/com/github/gotify/api/Callback.kt

@@ -10,7 +10,7 @@ internal class Callback<T> private constructor(
     private val onError: ErrorCallback
 ) {
     fun interface SuccessCallback<T> {
-        fun onSuccess(data: T?)
+        fun onSuccess(data: T)
     }
 
     fun interface ErrorCallback {
@@ -20,7 +20,9 @@ internal class Callback<T> private constructor(
     private class RetrofitCallback<T>(private val callback: Callback<T>) : retrofit2.Callback<T> {
         override fun onResponse(call: Call<T>, response: Response<T>) {
             if (response.isSuccessful) {
-                callback.onSuccess.onSuccess(response.body())
+                callback.onSuccess.onSuccess(
+                    response.body() ?: throw ApiException("null response", response)
+                )
             } else {
                 callback.onError.onError(ApiException(response))
             }

app/src/main/java/com/github/gotify/init/InitializationActivity.kt

@@ -61,7 +61,7 @@ internal class InitializationActivity : AppCompatActivity() {
         ClientFactory.userApiWithToken(settings)
             .currentUser()
             .enqueue(
-                    Callback.callInUI(this, { if (it != null) authenticated(it) }) { apiException ->
+                Callback.callInUI(this, { authenticated(it) }) { apiException ->
                     failed(apiException)
                 }
             )

app/src/main/java/com/github/gotify/login/LoginActivity.kt

@@ -194,7 +194,7 @@ internal class LoginActivity : AppCompatActivity() {
             settings.url = url
             binding.checkurlProgress.visibility = View.GONE
             binding.checkurl.visibility = View.VISIBLE
-            binding.checkurl.text = getString(R.string.found_gotify_version, version?.version)
+            binding.checkurl.text = getString(R.string.found_gotify_version, version.version)
             binding.username.visibility = View.VISIBLE
             binding.username.requestFocus()
             binding.password.visibility = View.VISIBLE
@@ -254,7 +254,7 @@ internal class LoginActivity : AppCompatActivity() {
             val newClient = Client().name(nameProvider.text.toString())
             client.createService(ClientApi::class.java)
                 .createClient(newClient)
-                .enqueue(Callback.callInUI(this, { if (it != null) onCreatedClient(it) }) {
+                .enqueue(Callback.callInUI(this, { onCreatedClient(it) }) {
                     onFailedToCreateClient()
                 })
         }

app/src/main/java/com/github/gotify/messages/provider/ApplicationHolder.kt

@@ -19,12 +19,10 @@ internal class ApplicationHolder(private val activity: Activity, private val cli
         client.createService(ApplicationApi::class.java)
             .apps
             .enqueue(
-                Callback.callInUI(
-                    activity,
-                    { apps: List<Application>? ->
-                        if (apps != null) onReceiveApps(apps)
+                Callback.callInUI(activity, { onReceiveApps(it) }) { e: ApiException ->
+                    onFailedApps(e)
                 }
-                ) { e: ApiException -> onFailedApps(e) })
+            )
     }
 
     private fun onReceiveApps(apps: List<Application>) {

app/src/main/java/com/github/gotify/service/WebSocketService.kt

@@ -80,7 +80,7 @@ internal class WebSocketService : Service() {
         showForegroundNotification(getString(R.string.websocket_init))
 
         if (lastReceivedMessage.get() == NOT_LOADED) {
-            missingMessageUtil.lastReceivedMessage { lastReceivedMessage.set(it ?: 0L) }
+            missingMessageUtil.lastReceivedMessage { lastReceivedMessage.set(it) }
         }
 
         val cm = getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager
@@ -97,7 +97,7 @@ internal class WebSocketService : Service() {
             .onClose { onClose() }
             .onBadRequest { message -> onBadRequest(message) }
             .onNetworkFailure { minutes -> onNetworkFailure(minutes) }
-            .onMessage { if (it != null) onMessage(it) }
+            .onMessage { onMessage(it) }
             .onReconnected { notifyMissedNotifications() }
             .start()