diff --git a/OF DL/Crypto/Padding.cs b/OF DL/Crypto/Padding.cs
index 1225e1e..5f4641b 100644
--- a/OF DL/Crypto/Padding.cs	
+++ b/OF DL/Crypto/Padding.cs	
@@ -37,7 +37,7 @@ public class Padding
         return result;
     }
 
-    public static byte[] AddPSSPadding(byte[] hash)
+    public static byte[]? AddPSSPadding(byte[] hash)
     {
         int modBits = 2048;
         int hLen = 20;
diff --git a/OF DL/Helpers/IFileNameHelper.cs b/OF DL/Helpers/IFileNameHelper.cs
index 6454742..0ea39f1 100644
--- a/OF DL/Helpers/IFileNameHelper.cs	
+++ b/OF DL/Helpers/IFileNameHelper.cs	
@@ -5,5 +5,5 @@ public interface IFileNameHelper
     Task<string> BuildFilename(string fileFormat, Dictionary<string, string> values);
 
     Task<Dictionary<string, string>> GetFilename(object obj1, object obj2, object obj3, List<string> selectedProperties,
-        string username, Dictionary<string, long> users = null);
+        string username, Dictionary<string, long>? users);
 }
diff --git a/OF DL/Services/APIService.cs b/OF DL/Services/APIService.cs
index 80edeb4..9c64c1d 100644
--- a/OF DL/Services/APIService.cs	
+++ b/OF DL/Services/APIService.cs	
@@ -125,7 +125,7 @@ public class APIService(IAuthService authService, IConfigService configService,
 
         try
         {
-            UserEntities.User? user = new();
+            UserEntities.User user = new();
             int post_limit = 50;
             Dictionary<string, string> getParams = new()
             {
@@ -166,7 +166,7 @@ public class APIService(IAuthService authService, IConfigService configService,
         return null;
     }
 
-    public async Task<JObject> GetUserInfoById(string endpoint)
+    public async Task<JObject?> GetUserInfoById(string endpoint)
     {
         try
         {
@@ -231,7 +231,7 @@ public class APIService(IAuthService authService, IConfigService configService,
     }
 
 
-    public async Task<Dictionary<string, long>> GetLists(string endpoint)
+    public async Task<Dictionary<string, long>?> GetLists(string endpoint)
     {
         Log.Debug("Calling GetLists");
 
@@ -358,7 +358,7 @@ public class APIService(IAuthService authService, IConfigService configService,
     }
 
 
-    public async Task<Dictionary<long, string>> GetMedia(MediaType mediatype,
+    public async Task<Dictionary<long, string>?> GetMedia(MediaType mediatype,
         string endpoint,
         string? username,
         string folder,
diff --git a/OF DL/Services/DownloadService.cs b/OF DL/Services/DownloadService.cs
index da1b941..eb2c698 100644
--- a/OF DL/Services/DownloadService.cs	
+++ b/OF DL/Services/DownloadService.cs	
@@ -576,7 +576,10 @@ public class DownloadService(
         using HttpResponseMessage response = await client.GetAsync(mpdURL, HttpCompletionOption.ResponseHeadersRead);
         if (response.IsSuccessStatusCode)
         {
-            return response.Content.Headers.LastModified.Value.DateTime;
+            if (response.Content.Headers.LastModified != null)
+            {
+                return response.Content.Headers.LastModified.Value.DateTime;
+            }
         }
 
         return DateTime.Now;
diff --git a/OF DL/Services/IAPIService.cs b/OF DL/Services/IAPIService.cs
index a14c024..fe55d1f 100644
--- a/OF DL/Services/IAPIService.cs	
+++ b/OF DL/Services/IAPIService.cs	
@@ -16,10 +16,10 @@ public interface IAPIService
     Task<string> GetDecryptionKeyCDM(Dictionary<string, string> drmHeaders, string licenceURL, string pssh);
     Task<DateTime> GetDRMMPDLastModified(string mpdUrl, string policy, string signature, string kvp);
     Task<string> GetDRMMPDPSSH(string mpdUrl, string policy, string signature, string kvp);
-    Task<Dictionary<string, long>> GetLists(string endpoint);
-    Task<List<string>> GetListUsers(string endpoint);
+    Task<Dictionary<string, long>?> GetLists(string endpoint);
+    Task<List<string>?> GetListUsers(string endpoint);
 
-    Task<Dictionary<long, string>> GetMedia(MediaType mediatype, string endpoint, string? username, string folder,
+    Task<Dictionary<long, string>?> GetMedia(MediaType mediatype, string endpoint, string? username, string folder,
         List<long> paid_post_ids);
 
     Task<PurchasedEntities.PaidPostCollection> GetPaidPosts(string endpoint, string folder, string username,
@@ -46,10 +46,10 @@ public interface IAPIService
     Task<List<PurchasedEntities.PurchasedTabCollection>> GetPurchasedTab(string endpoint, string folder,
         Dictionary<string, long> users);
 
-    Task<UserEntities.User> GetUserInfo(string endpoint);
-    Task<JObject> GetUserInfoById(string endpoint);
+    Task<UserEntities.User?> GetUserInfo(string endpoint);
+    Task<JObject?> GetUserInfoById(string endpoint);
     Dictionary<string, string> GetDynamicHeaders(string path, string queryParam);
-    Task<Dictionary<string, long>> GetActiveSubscriptions(string endpoint, bool includeRestrictedSubscriptions);
-    Task<Dictionary<string, long>> GetExpiredSubscriptions(string endpoint, bool includeRestrictedSubscriptions);
+    Task<Dictionary<string, long>?> GetActiveSubscriptions(string endpoint, bool includeRestrictedSubscriptions);
+    Task<Dictionary<string, long>?> GetExpiredSubscriptions(string endpoint, bool includeRestrictedSubscriptions);
     Task<string> GetDecryptionKeyOFDL(Dictionary<string, string> drmHeaders, string licenceURL, string pssh);
 }
diff --git a/OF DL/Utils/HttpUtil.cs b/OF DL/Utils/HttpUtil.cs
index eaa7ebb..bd0203a 100644
--- a/OF DL/Utils/HttpUtil.cs	
+++ b/OF DL/Utils/HttpUtil.cs	
@@ -54,7 +54,7 @@ internal class HttpUtil
         return bytes;
     }
 
-    public static async Task<string> GetWebSource(string URL, Dictionary<string, string> headers = null)
+    public static async Task<string> GetWebSource(string URL, Dictionary<string, string>? headers = null)
     {
         HttpResponseMessage response = await PerformOperation(async () => { return await Get(URL, headers); });
 
@@ -62,7 +62,7 @@ internal class HttpUtil
         return Encoding.UTF8.GetString(bytes);
     }
 
-    public static async Task<byte[]> GetBinary(string URL, Dictionary<string, string> headers = null)
+    public static async Task<byte[]> GetBinary(string URL, Dictionary<string, string>? headers = null)
     {
         HttpResponseMessage response = await PerformOperation(async () => { return await Get(URL, headers); });
 
@@ -72,7 +72,7 @@ internal class HttpUtil
 
     public static string GetString(byte[] bytes) => Encoding.UTF8.GetString(bytes);
 
-    private static async Task<HttpResponseMessage> Get(string URL, Dictionary<string, string> headers = null)
+    private static async Task<HttpResponseMessage> Get(string URL, Dictionary<string, string>? headers = null)
     {
         HttpRequestMessage request = new() { RequestUri = new Uri(URL), Method = HttpMethod.Get };
 
@@ -87,8 +87,8 @@ internal class HttpUtil
         return await Send(request);
     }
 
-    private static async Task<HttpResponseMessage> Post(string URL, Dictionary<string, string> headers,
-        HttpContent content)
+    private static async Task<HttpResponseMessage> Post(string URL, Dictionary<string, string>? headers = null,
+        HttpContent? content = null)
     {
         HttpRequestMessage request = new() { RequestUri = new Uri(URL), Method = HttpMethod.Post, Content = content };
 
diff --git a/OF DL/Widevine/CDM.cs b/OF DL/Widevine/CDM.cs
index d005cd5..64e352c 100644
--- a/OF DL/Widevine/CDM.cs	
+++ b/OF DL/Widevine/CDM.cs	
@@ -48,7 +48,7 @@ public class CDM
         return pssh;
     }
 
-    public static string OpenSession(string initDataB64, string deviceName, bool offline = false, bool raw = false)
+    public static string? OpenSession(string initDataB64, string deviceName, bool offline = false, bool raw = false)
     {
         byte[] initData = CheckPSSH(initDataB64);
 
@@ -98,7 +98,7 @@ public class CDM
         return BytesToHex(sessionId);
     }
 
-    private static WidevineCencHeader ParseInitData(byte[] initData)
+    private static WidevineCencHeader? ParseInitData(byte[] initData)
     {
         WidevineCencHeader cencHeader;
 
@@ -190,7 +190,7 @@ public class CDM
         return true;
     }
 
-    public static byte[] GetLicenseRequest(string sessionId)
+    public static byte[]? GetLicenseRequest(string sessionId)
     {
         //Logger.Debug($"GetLicenseRequest(sessionId={BytesToHex(sessionId)})");
         //Logger.Verbose($"Getting license request");
diff --git a/OF DL/Widevine/CDMDevice.cs b/OF DL/Widevine/CDMDevice.cs
index 887a91f..61ba112 100644
--- a/OF DL/Widevine/CDMDevice.cs	
+++ b/OF DL/Widevine/CDMDevice.cs	
@@ -11,8 +11,8 @@ namespace OF_DL.Widevine;
 
 public class CDMDevice
 {
-    public CDMDevice(string deviceName, byte[] clientIdBlobBytes = null, byte[] privateKeyBytes = null,
-        byte[] vmpBytes = null)
+    public CDMDevice(string deviceName, byte[]? clientIdBlobBytes = null, byte[]? privateKeyBytes = null,
+        byte[]? vmpBytes = null)
     {
         DeviceName = deviceName;
 
diff --git a/OF DL/Widevine/ContentKey.cs b/OF DL/Widevine/ContentKey.cs
index 3a25f9d..2487f56 100644
--- a/OF DL/Widevine/ContentKey.cs	
+++ b/OF DL/Widevine/ContentKey.cs	
@@ -6,11 +6,11 @@ namespace OF_DL.Widevine;
 [Serializable]
 public class ContentKey
 {
-    [JsonPropertyName("key_id")] public byte[] KeyID { get; set; }
+    [JsonPropertyName("key_id")] public byte[] KeyID { get; set; } = [];
 
-    [JsonPropertyName("type")] public string Type { get; set; }
+    [JsonPropertyName("type")] public string Type { get; set; } = "";
 
-    [JsonPropertyName("bytes")] public byte[] Bytes { get; set; }
+    [JsonPropertyName("bytes")] public byte[] Bytes { get; set; } = [];
 
     [NotMapped]
     [JsonPropertyName("permissions")]
@@ -20,7 +20,7 @@ public class ContentKey
         set => PermissionsString = string.Join(",", value);
     }
 
-    [JsonIgnore] public string PermissionsString { get; set; }
+    [JsonIgnore] public string PermissionsString { get; set; } = "";
 
     public override string ToString() =>
         $"{BitConverter.ToString(KeyID).Replace("-", "").ToLower()}:{BitConverter.ToString(Bytes).Replace("-", "").ToLower()}";
diff --git a/OF DL/Widevine/DerivedKeys.cs b/OF DL/Widevine/DerivedKeys.cs
index 9aca670..2ca9d1d 100644
--- a/OF DL/Widevine/DerivedKeys.cs	
+++ b/OF DL/Widevine/DerivedKeys.cs	
@@ -2,7 +2,7 @@ namespace OF_DL.Widevine;
 
 public class DerivedKeys
 {
-    public byte[] Auth1 { get; set; }
-    public byte[] Auth2 { get; set; }
-    public byte[] Enc { get; set; }
+    public byte[] Auth1 { get; set; } = [];
+    public byte[] Auth2 { get; set; } = [];
+    public byte[] Enc { get; set; } = [];
 }
diff --git a/OF DL/Widevine/PSSHBox.cs b/OF DL/Widevine/PSSHBox.cs
index 64363d6..0e59099 100644
--- a/OF DL/Widevine/PSSHBox.cs	
+++ b/OF DL/Widevine/PSSHBox.cs	
@@ -57,7 +57,7 @@ internal class PSSHBox
 
         if (dataLength == 0)
         {
-            return new PSSHBox(kids, null);
+            return new PSSHBox(kids, []);
         }
 
         byte[] data = new byte[dataLength];
diff --git a/OF DL/Widevine/Session.cs b/OF DL/Widevine/Session.cs
index e9177ef..d879aa5 100644
--- a/OF DL/Widevine/Session.cs	
+++ b/OF DL/Widevine/Session.cs	
@@ -1,24 +1,16 @@
 namespace OF_DL.Widevine;
 
-internal class Session
+internal class Session(byte[] sessionId, dynamic initData, CDMDevice device, bool offline)
 {
-    public Session(byte[] sessionId, dynamic initData, CDMDevice device, bool offline)
-    {
-        SessionId = sessionId;
-        InitData = initData;
-        Offline = offline;
-        Device = device;
-    }
-
-    public byte[] SessionId { get; set; }
-    public dynamic InitData { get; set; }
-    public bool Offline { get; set; }
-    public CDMDevice Device { get; set; }
-    public byte[] SessionKey { get; set; }
-    public DerivedKeys DerivedKeys { get; set; }
-    public byte[] LicenseRequest { get; set; }
-    public SignedLicense License { get; set; }
-    public SignedDeviceCertificate ServiceCertificate { get; set; }
+    public byte[] SessionId { get; set; } = sessionId;
+    public dynamic InitData { get; set; } = initData;
+    public bool Offline { get; set; } = offline;
+    public CDMDevice Device { get; set; } = device;
+    public byte[] SessionKey { get; set; } = [];
+    public DerivedKeys DerivedKeys { get; set; } = new();
+    public byte[] LicenseRequest { get; set; } = [];
+    public SignedLicense License { get; set; } = new();
+    public SignedDeviceCertificate ServiceCertificate { get; set; } = new();
     public bool PrivacyMode { get; set; }
-    public List<ContentKey> ContentKeys { get; set; } = new();
+    public List<ContentKey> ContentKeys { get; set; } = [];
 }