autofill: avoid crash when looking up a null key.

closes https://github.com/PhilippC/keepass2android/issues/2362

src/Kp2aAutofillParser/AutofillParser.cs

@@ -445,6 +445,9 @@ namespace Kp2aAutofillParser
 
         public static string ToCanonicalHint(string hint)
         {
+            //avoid crash when looking up a null key
+            if (hint == null)
+                return "";
             string canonicalHint;
             if (!hintToCanonicalReplacement.TryGetValue(hint, out canonicalHint))
                 canonicalHint = hint;
@@ -841,6 +844,7 @@ namespace Kp2aAutofillParser
                         continue;
                     if (viewHints.Where(h => h != null).Select(AutofillHintsHelper.ToCanonicalHint).Intersect(_autofillHintsForLogin).Any())
                     {
+
                         AddFieldToHintMap(viewNode, viewHints.Where(h => h != null).Select(AutofillHintsHelper.ToCanonicalHint).ToHashSet().ToArray());
                     }
 

src/keepass2android-app/NullActivity.cs

@@ -0,0 +1,24 @@
+using Android.Content.PM;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace keepass2android
+{
+    [Activity(Label = AppNames.AppName,
+        MainLauncher = false,
+        Theme = "@style/Kp2aTheme_BlueNoActionBar",
+        Exported = true)] 
+    ///For autofill, we sometimes need to pass an intent to an inline presentation which never gets fired. We use this as a dummy activity.
+    public class NullActivity: Activity
+    {
+        protected override void OnCreate(Bundle savedInstanceState)
+        {
+            Kp2aLog.Log("NullActivity.OnCreate - this is unexpected.");
+            base.OnCreate(savedInstanceState);
+            Finish();
+        }
+    }
+}

src/keepass2android-app/services/AutofillBase/AutofillHelper.cs

@@ -30,10 +30,9 @@ namespace keepass2android.services.AutofillBase
             {
                 return null;
             }
-            //make sure we have a pendingIntent always not null
-            pendingIntent ??= PendingIntent.GetService(context, 0, new Intent(),
-                Util.AddMutabilityFlag(PendingIntentFlags.OneShot | PendingIntentFlags.UpdateCurrent, PendingIntentFlags.Mutable));
-            
+            // If the pending intent is null, we need to create a dummy one to avoid a crash
+            pendingIntent ??= PendingIntent.GetActivity(context, 0, new Intent(context, typeof(NullActivity)), PendingIntentFlags.OneShot | PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable);
+
             var slice = CreateInlinePresentationSlice(
                 inlinePresentationSpec,
                 text,

src/keepass2android-app/services/AutofillBase/AutofillServiceBase.cs

@@ -405,7 +405,7 @@ namespace keepass2android.services.AutofillBase
             var datasetBuilder = new Dataset.Builder(presentation);
             datasetBuilder.SetAuthentication(pendingIntent?.IntentSender);
 
-            AutofillHelper.AddInlinePresentation(this, inlinePresentationSpec, text, datasetBuilder, Resource.Drawable.baseline_close_24, null);
+            AutofillHelper.AddInlinePresentation(this, inlinePresentationSpec, text, datasetBuilder, Resource.Drawable.baseline_close_24, pendingIntent);
 
             foreach (var autofillId in autofillIds)
             {