Feature/potential fix for android il2cpp crash (#135)

* Skip null items when converting collections to dtos

* Experimental fix for Ticket(38178) - TrySaveToDtoDictionary crash on Android(7, 10, 11, 12) & IL2CPP

* use TrySaveToDto + improve comment

Author: sierpinskid

Assets/Plugins/StreamChat/Core/LowLevelClient/Requests/UpdateUsersRequest.cs

@@ -1,4 +1,5 @@
-using StreamChat.Core.Helpers;
+using System.Collections.Generic;
+using StreamChat.Core.Helpers;
 using StreamChat.Core.InternalDTO.Requests;
 
 namespace StreamChat.Core.LowLevelClient.Requests
@@ -11,11 +12,39 @@ public partial class UpdateUsersRequest : RequestObjectBase, ISavableTo<UpdateUs
         /// StreamTodo: Check if this could be list
         public System.Collections.Generic.Dictionary<string, UserObjectRequest> Users { get; set; }
 
-        UpdateUsersRequestInternalDTO ISavableTo<UpdateUsersRequestInternalDTO>.SaveToDto() =>
-            new UpdateUsersRequestInternalDTO
+        UpdateUsersRequestInternalDTO ISavableTo<UpdateUsersRequestInternalDTO>.SaveToDto()
+        {
+            var dto = new UpdateUsersRequestInternalDTO
             {
-                Users = Users.TrySaveToDtoDictionary<UserObjectRequestInternalDTO, UserObjectRequest, string>(),
+                // Users = Users.TrySaveToDtoDictionary<UserObjectRequestInternalDTO, UserObjectRequest, string>(),
                 AdditionalProperties = AdditionalProperties,
             };
+
+            // Ticket#38178 TrySaveToDtoDictionary caused crashes on old Android versions with IL2CPP
+            // Perhaps this due to IL2CPP not handling well complex generic signatures
+            if (Users != null)
+            {
+                var dict = new Dictionary<string, UserObjectRequestInternalDTO>();
+            
+                foreach (var sourceKeyValue in Users)
+                {
+                    if (sourceKeyValue.Value == null)
+                    {
+                        continue;
+                    }
+
+                    var serialized = sourceKeyValue.Value.TrySaveToDto();
+
+                    if (serialized != null)
+                    {
+                        dict.Add(sourceKeyValue.Key,serialized);
+                    }
+                }
+            
+                dto.Users = dict;
+            }
+
+            return dto;
+        }
     }
 }