cleanup C# SDK [#11]

Author: dnl-blkv

BunqSdk/Json/InstallationConverter.cs

@@ -25,14 +25,19 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
             JsonSerializer serializer)
         {
             var jObjects = JArray.Load(reader).ToObject<List<JObject>>();
-            var id = jObjects[INDEX_ID].GetValue(FIELD_ID).ToObject<Id>();
-            var token = jObjects[INDEX_TOKEN].GetValue(FIELD_TOKEN).ToObject<SessionToken>();
-            var publicKeyServer = jObjects[INDEX_SERVER_PUBLIC_KEY].GetValue(FIELD_SERVER_PUBLIC_KEY)
-                .ToObject<PublicKeyServer>();
+            var id = FetchObject<Id>(jObjects[INDEX_ID], FIELD_ID);
+            var token = FetchObject<SessionToken>(jObjects[INDEX_TOKEN], FIELD_TOKEN);
+            var publicKeyServer =
+                FetchObject<PublicKeyServer>(jObjects[INDEX_SERVER_PUBLIC_KEY], FIELD_SERVER_PUBLIC_KEY);
 
             return new Installation(id, token, publicKeyServer);
         }
 
+        private static T FetchObject<T>(JToken jToken, string fieldName)
+        {
+            return jToken[fieldName].ToObject<T>();
+        }
+
         public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
         {
             throw new NotImplementedException();

BunqSdk/Model/BunqModel.cs

@@ -16,6 +16,11 @@ public abstract class BunqModel
         private const string FIELD_ID = "Id";
         private const string FIELD_UUID = "Uuid";
 
+        /// <summary>
+        /// Index of the very first item in an array.
+        /// </summary>
+        private const int INDEX_FIRST = 0;
+
         /// <summary>
         /// De-serializes an object from a JSON format specific to Installation and SessionServer.
         /// </summary>
@@ -46,7 +51,7 @@ private static JObject GetResponseContent(BunqResponseRaw responseRaw)
             var json = Encoding.UTF8.GetString(responseRaw.BodyBytes);
             var responseWithWrapper = BunqJsonConvert.DeserializeObject<JObject>(json);
 
-            return responseWithWrapper.GetValue(FIELD_RESPONSE).ToObject<JArray>().Value<JObject>(0);
+            return responseWithWrapper.GetValue(FIELD_RESPONSE).ToObject<JArray>().Value<JObject>(INDEX_FIRST);
         }
 
         private static string GetWrappedContentString(JObject json, string wrapper)