fix: failure to get series if no items (#749)

If there was no items in a series list (such as anime), then the call to retrieve the series would
fail. Instead make it return an empty list but still a successful request. This fixes the issue of
if a user has only anime in their library, or only manga.

fix #746

libraries/kitsu/library/src/main/java/com/chesire/nekome/kitsu/library/KitsuLibrary.kt

@@ -139,10 +139,7 @@ class KitsuLibrary @Inject constructor(
 
             val body = response.body()
             if (response.isSuccessful && body != null) {
-                val series = body.data.mapNotNull {
-                    map.toSeriesDomain(AddResponseDto(it, body.included))
-                }
-                models.addAll(series)
+                models.addAll(buildSeries(body))
                 retries = 0
 
                 if (body.links.next.isNotEmpty()) {
@@ -167,6 +164,16 @@ class KitsuLibrary @Inject constructor(
         }
     }
 
+    private fun buildSeries(body: RetrieveResponseDto): List<SeriesDomain> {
+        return body.data.mapNotNull {
+            if (body.included == null) {
+                null
+            } else {
+                map.toSeriesDomain(AddResponseDto(it, body.included))
+            }
+        }
+    }
+
     private fun parseResponse(response: Response<AddResponseDto>): Resource<SeriesDomain> {
         return if (response.isSuccessful) {
             response.body()?.let { entity ->

libraries/kitsu/library/src/main/java/com/chesire/nekome/kitsu/library/dto/RetrieveResponseDto.kt

@@ -12,7 +12,7 @@ data class RetrieveResponseDto(
     @Json(name = "data")
     val data: List<DataDto>,
     @Json(name = "included")
-    val included: List<IncludedDto>,
+    val included: List<IncludedDto>?,
     @Json(name = "links")
     val links: Links
 )