Fix compiler errors for Unity 2019.4 (#137)

* Fix compiler errors for Unity 2019.4

* prevent Json from IL2CPP code stripping (tested on 2019.4 IL2CPP, .NET Standard 2.0)

Author: sierpinskid

Assets/Plugins/StreamChat/Core/LowLevelClient/API/Internal/InternalApiClientBase.cs

@@ -96,7 +96,11 @@ private async Task<TResponse> HttpRequest<TResponse>(HttpMethodType httpMethod,
 
             if (httpMethod == HttpMethodType.Get && serializedContent != null)
             {
-                queryParameters ??= QueryParameters.Default;
+                if (queryParameters == null)
+                {
+                    queryParameters = QueryParameters.Default;
+                }
+
                 queryParameters.Append("payload", serializedContent);
             }
 

Assets/Plugins/StreamChat/Core/LowLevelClient/StreamChatLowLevelClient.cs

@@ -205,7 +205,11 @@ private set
         public static IStreamChatLowLevelClient CreateDefaultClient(AuthCredentials authCredentials,
             IStreamClientConfig config = default)
         {
-            config ??= StreamClientConfig.Default;
+            if (config == null)
+            {
+                config = StreamClientConfig.Default;
+            }
+            
             var logs = StreamDependenciesFactory.CreateLogger(config.LogLevel.ToLogLevel());
             var applicationInfo = StreamDependenciesFactory.CreateApplicationInfo();
             var websocketClient

Assets/Plugins/StreamChat/Core/Responses/StreamFileUploadResponse.cs

@@ -2,7 +2,7 @@ namespace StreamChat.Core.Responses
 {
     public readonly struct StreamFileUploadResponse
     {
-        public readonly string FileUrl { get; }
+        public string FileUrl { get; }
 
         internal StreamFileUploadResponse(string fileUrl)
         {

Assets/Plugins/StreamChat/Core/StatefulModels/StreamChannel.cs

@@ -290,7 +290,10 @@ public async Task<IEnumerable<IStreamChannelMember>> QueryMembersAsync(
             IDictionary<string, object> filters = null, int limit = 30, int offset = 0)
         {
             // filter_conditions is required by API but empty object is accepted
-            filters ??= new Dictionary<string, object>();
+            if (filters == null)
+            {
+                filters = new Dictionary<string, object>();
+            }
 
             var response = await LowLevelClient.InternalChannelApi.QueryMembersAsync(new QueryMembersRequestInternalDTO
             {

Assets/Plugins/StreamChat/Core/StreamChatClient.cs

@@ -94,7 +94,11 @@ public sealed class StreamChatClient : IStreamChatClient
         /// <param name="config">[Optional] configuration</param>
         public static IStreamChatClient CreateDefaultClient(IStreamClientConfig config = default)
         {
-            config ??= StreamClientConfig.Default;
+            if (config == null)
+            {
+                config = StreamClientConfig.Default;
+            }
+            
             var logs = StreamDependenciesFactory.CreateLogger(config.LogLevel.ToLogLevel());
             var websocketClient
                 = StreamDependenciesFactory.CreateWebsocketClient(logs, config.LogLevel.IsDebugEnabled());

Assets/Plugins/StreamChat/EditorTools/DefineSymbols/Unity2020DefineSymbols.cs

@@ -1,6 +1,5 @@
-#if UNITY_2020_1_OR_NEWER && !UNITY_2021
+#if UNITY_2019_1_OR_NEWER && !UNITY_2021_1_OR_NEWER
 using System.Collections.Generic;
-using System.Linq;
 using UnityEditor;
 
 namespace StreamChat.EditorTools.DefineSymbols

Assets/Plugins/StreamChat/EditorTools/DefineSymbols/Unity2021DefineSymbols.cs

@@ -1,4 +1,4 @@
-#if UNITY_2021
+#if UNITY_2021_1_OR_NEWER
 using System.Collections.Generic;
 using UnityEditor;
 using UnityEditor.Build;

Assets/Plugins/StreamChat/EditorTools/DefineSymbols/UnityDefineSymbolsFactory.cs

@@ -4,7 +4,7 @@ public class UnityDefineSymbolsFactory
     {
         public IUnityDefineSymbols CreateDefault()
         {
-#if UNITY_2021
+#if UNITY_2021_1_OR_NEWER
             return new Unity2021DefineSymbols();
 #else
             return new Unity2020DefineSymbols();

Assets/Plugins/StreamChat/Libs/Auth/ITokenProvider.cs

@@ -1,5 +1,4 @@
 using System.Threading.Tasks;
-using UnityEngine;
 
 namespace StreamChat.Libs.Auth
 {
@@ -14,4 +13,6 @@ public interface ITokenProvider
         /// <remarks>https://getstream.io/chat/docs/unity/tokens_and_authentication/?language=unity#token-providers</remarks>
         Task<string> GetTokenAsync(string userId);
     }
+    
+    //StreamTodo: we could split this into IAsyncTokenProvider for async/await syntax and IEnumeratorTokenProvider for coroutines? 
 }

Assets/Plugins/StreamChat/Libs/Http/HttpResponse.cs

@@ -1,5 +1,6 @@
 using System.Net.Http;
 using System.Threading.Tasks;
+using StreamChat.Libs.Utils;
 using UnityEngine.Networking;
 
 namespace StreamChat.Libs.Http
@@ -22,9 +23,8 @@ public static async Task<HttpResponse> CreateFromHttpResponseMessageAsync(
 
         public static HttpResponse CreateFromUnityWebRequest(UnityWebRequest unityWebRequest)
         {
-            var isSuccessStatusCode = unityWebRequest.result == UnityWebRequest.Result.Success;
             var result = unityWebRequest.downloadHandler?.text ?? string.Empty;
-            return new HttpResponse(isSuccessStatusCode, (int)unityWebRequest.responseCode, result);
+            return new HttpResponse(unityWebRequest.IsRequestSuccessful(), (int)unityWebRequest.responseCode, result);
         }
 
         public HttpResponse(bool isSuccessStatusCode, int statusCode, string result)