Turns out Koin can't inject null

Fix #23

favorites/src/main/java/de/mm20/launcher2/favorites/FavoritesItem.kt

@@ -18,20 +18,16 @@ data class FavoritesItem(
     var pinPosition: Int,
     var hidden: Boolean
 ) : KoinComponent {
-    private val serializer: SearchableSerializer? by inject { parametersOf(searchable) }
+    private val serializer: SearchableSerializer by inject { parametersOf(searchable) }
 
     fun toDatabaseEntity(): FavoritesItemEntity? {
-        val serializer = serializer ?: return null
+        val serializer = serializer
+
+        val data = searchable?.let { serializer.serialize(it) } ?: return null
 
         return FavoritesItemEntity(
             key = key,
-            serializedSearchable = searchable?.let {
-                "${serializer.typePrefix}#${
-                    serializer.serialize(
-                        it
-                    )
-                }"
-            } ?: "",
+            serializedSearchable = "${serializer.typePrefix}#${data}",
             hidden = hidden,
             pinPosition = pinPosition,
             launchCount = launchCount

favorites/src/main/java/de/mm20/launcher2/favorites/Module.kt

@@ -6,6 +6,7 @@ import de.mm20.launcher2.contacts.ContactDeserializer
 import de.mm20.launcher2.contacts.ContactSerializer
 import de.mm20.launcher2.files.*
 import de.mm20.launcher2.search.NullDeserializer
+import de.mm20.launcher2.search.NullSerializer
 import de.mm20.launcher2.search.data.*
 import de.mm20.launcher2.websites.WebsiteDeserializer
 import de.mm20.launcher2.websites.WebsiteSerializer
@@ -50,7 +51,7 @@ val favoritesModule = module {
         if (searchable is Website) {
             return@factory WebsiteSerializer()
         }
-        return@factory null
+        return@factory NullSerializer()
     }
 
     factory { (serialized: String) ->

search/src/main/java/de/mm20/launcher2/search/SearchableSerializer.kt

@@ -3,6 +3,16 @@ package de.mm20.launcher2.search
 import de.mm20.launcher2.search.data.Searchable
 
 interface SearchableSerializer {
-    fun serialize(searchable: Searchable): String
+    fun serialize(searchable: Searchable): String?
     val typePrefix: String
+}
+
+class NullSerializer : SearchableSerializer {
+    override fun serialize(searchable: Searchable): String? {
+        return null
+    }
+
+    override val typePrefix: String
+        get() = "null"
+
 }