add nullchecks for user's entry in login and register pages

Controllers/ConnectionController.cs

@@ -14,6 +14,16 @@ namespace ShoopNCook.Controllers
 
         public void Login(string email, string password)
         {
+            if (email == null)
+            {
+                UserNotifier.Notice("Please provide an email address");
+                return;
+            }
+            if (password == null)
+            {
+                UserNotifier.Notice("Please provide your password");
+                return;
+            }
             Account? acc = accounts.Login(email, password);    
             if (acc == null)
             {
@@ -25,6 +35,21 @@ namespace ShoopNCook.Controllers
 
         public void Register(string username, string email, string password)
         {
+            if (email == null)
+            {
+                UserNotifier.Notice("Please provide an email address");
+                return;
+            }
+            if (password == null)
+            {
+                UserNotifier.Notice("Please provide your password");
+                return;
+            }
+            if (username == null)
+            {
+                UserNotifier.Notice("Please provide an username");
+                return;
+            }
             Account? acc = accounts.Register(username, email, password);
             if (acc == null)
             {

Views/CreateRecipePage.xaml.cs

@@ -16,21 +16,21 @@ public partial class CreateRecipePage : ContentPage
         this.onRecipeCreated = onRecipeCreated;
 	}
 
-    private async void OnAddIngredientTapped(object sender, TappedEventArgs e)
+    private void OnAddIngredientTapped(object sender, TappedEventArgs e)
     {
         IngredientList.Children.Add(new IngredientEntry());
     }
 
-    private async void OnAddStepTapped(object sender, TappedEventArgs e)
+    private void OnAddStepTapped(object sender, TappedEventArgs e)
     {
         StepList.Children.Add(new StepEntry((uint) StepList.Children.Count() + 1));
     }
     private async void OnBackButtonClicked(object sender, EventArgs e)
     {
-        Navigation.PopAsync();
+        await Navigation.PopAsync();
     }
 
-    private async void OnUploadRecipeClicked(object sender, EventArgs e)
+    private void OnUploadRecipeClicked(object sender, EventArgs e)
     {
 
         uint callPerPers;

Views/FavoritesPage.xaml.cs

@@ -29,13 +29,13 @@ public partial class FavoritesPage : ContentPage
         {
             RecipeViewLayout.Children.Add(new RecipeView(info, async () =>
             {
-                Recipe? recipe = service.GetRecipe(info);
+                Recipe recipe = service.GetRecipe(info);
                 await Shell.Current.Navigation.PushAsync(new RecipePage(recipe, preferences, 1));
             }));
         });
     }
 
-    private async void ContentPage_NavigatedTo(object sender, NavigatedToEventArgs e)
+    private void ContentPage_NavigatedTo(object sender, NavigatedToEventArgs e)
     {
         UpdateFavorites();
     }

Views/HomePage.xaml.cs

@@ -19,7 +19,7 @@ public partial class HomePage : ContentPage
         {
             layout.Children.Add(new RecipeView(info, () =>
             {
-                Recipe? recipe = service.GetRecipe(info);
+                Recipe recipe = service.GetRecipe(info);
                 if (recipe != null)
                     Shell.Current.Navigation.PushAsync(new RecipePage(recipe, preferences, 1));
                 else
@@ -36,9 +36,6 @@ public partial class HomePage : ContentPage
         ProfilePictureName.Text = account.User.Name;
 	}
 
-
-    
-
     private async void OnSyncButtonClicked(object sender, EventArgs e)
     {
         await Shell.Current.Navigation.PushAsync(new SearchPage());

Views/LoginPage.xaml.cs

@@ -11,7 +11,7 @@ public partial class LoginPage : ContentPage
 		InitializeComponent();
         this.controller = controller;
 	}
-    private async void OnLoginButtonClicked(object sender, EventArgs e)
+    private void OnLoginButtonClicked(object sender, EventArgs e)
     {
         string email = EmailEntry.Text;
         string password = PasswordEntry.Text;