Make MusicFolder has default values.

Signed-off-by: Yahor Berdnikau <egorr.berd@gmail.com>

subsonic-api/src/integrationTest/kotlin/org/moire/ultrasonic/api/subsonic/SubsonicAPIClientTest.kt

@@ -146,7 +146,7 @@ class SubsonicAPIClientTest {
     fun `Should parse get music folders error response`() {
         val response = checkErrorCallParsed { client.api.getMusicFolders().execute() }
 
-        response.musicFolders `should be` null
+        response.musicFolders `should equal` emptyList()
     }
 
     @Test

subsonic-api/src/main/kotlin/org/moire/ultrasonic/api/subsonic/models/MusicFolder.kt

@@ -1,3 +1,3 @@
 package org.moire.ultrasonic.api.subsonic.models
 
-data class MusicFolder(val id: Long, val name: String)
+data class MusicFolder(val id: Long = -1, val name: String = "")

subsonic-api/src/main/kotlin/org/moire/ultrasonic/api/subsonic/response/MusicFoldersResponse.kt

@@ -14,7 +14,7 @@ class MusicFoldersResponse(status: Status,
                            version: SubsonicAPIVersions,
                            error: SubsonicError?,
                            @JsonDeserialize(using = MusicFoldersDeserializer::class)
-                           val musicFolders: List<MusicFolder>?):
+                           val musicFolders: List<MusicFolder> = emptyList()):
         SubsonicResponse(status, version, error) {
     companion object {
         class MusicFoldersDeserializer(): JsonDeserializer<List<MusicFolder>>() {

ultrasonic/src/main/kotlin/org/moire/ultrasonic/data/SubsonicAPIConverter.kt

@@ -0,0 +1,5 @@
+package org.moire.ultrasonic.data
+
+/**
+ * Created by egorr on 26.07.17.
+ */

ultrasonic/src/test/kotlin/org/moire/ultrasonic/data/APIConverterTest.kt

@@ -0,0 +1,8 @@
+package org.moire.ultrasonic.data
+
+import org.junit.Assert.*
+
+/**
+ * Created by egorr on 26.07.17.
+ */
+class APIConverterTest