diff --git a/S7.Net.UnitTest/S7NetTestsAsync.cs b/S7.Net.UnitTest/S7NetTestsAsync.cs
index 86d7f22..38f12af 100644
--- a/S7.Net.UnitTest/S7NetTestsAsync.cs
+++ b/S7.Net.UnitTest/S7NetTestsAsync.cs
@@ -591,15 +591,13 @@ namespace S7.Net.UnitTest
 
 
         [TestMethod]
-        [ExpectedException(typeof(NullReferenceException))]
         public async Task Test_Async_ReadBytesReturnsNullIfPlcIsNotConnected()
         {
             using (var notConnectedPlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 0))
             {
                 Assert.IsFalse(notConnectedPlc.IsConnected);
                 TestClass tc = new TestClass();
-                var res = await notConnectedPlc.ReadClassAsync(tc, DB2);
-                Assert.Fail();
+                await Assert.ThrowsExceptionAsync<PlcException>(async () => await notConnectedPlc.ReadClassAsync(tc, DB2));
             }
         }
 
@@ -637,13 +635,12 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        [ExpectedException(typeof(NullReferenceException))]
         public async Task Test_Async_ReadClassWithGenericReturnsNullIfPlcIsNotConnected()
         {
             using (var notConnectedPlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 0))
             {
                 Assert.IsFalse(notConnectedPlc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
-                TestClass tc = await notConnectedPlc.ReadClassAsync<TestClass>(DB2);
+                await Assert.ThrowsExceptionAsync<PlcException>(async () => await notConnectedPlc.ReadClassAsync<TestClass>(DB2));
             }
         }
 
@@ -678,13 +675,12 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        [ExpectedException(typeof(NullReferenceException))]
         public async Task Test_Async_ReadClassWithGenericAndClassFactoryThrowsExceptionPlcIsNotConnected()
         {
             using (var notConnectedPlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 0))
             {
                 Assert.IsFalse(notConnectedPlc.IsConnected);
-                TestClass tc = await notConnectedPlc.ReadClassAsync(() => new TestClass(), DB2);
+                await Assert.ThrowsExceptionAsync<PlcException>(async () => await notConnectedPlc.ReadClassAsync(() => new TestClass(), DB2));
             }
         }
 
@@ -711,13 +707,12 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        [ExpectedException(typeof(NullReferenceException))]
         public async Task Test_Async_ReadStructThrowsExceptionPlcIsNotConnected()
         {
             using (var notConnectedPlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 0))
             {
                 Assert.IsFalse(notConnectedPlc.IsConnected);
-                object tsObj = await notConnectedPlc.ReadStructAsync(typeof(TestStruct), DB2);
+                await Assert.ThrowsExceptionAsync<PlcException>(async () => await notConnectedPlc.ReadStructAsync(typeof(TestStruct), DB2));
             }
         }
 
@@ -754,13 +749,12 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        [ExpectedException(typeof(NullReferenceException))]
         public async Task Test_Async_ReadStructWithGenericThrowsExceptionIfPlcIsNotConnected()
         {
             using (var notConnectedPlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 0))
             {
                 Assert.IsFalse(notConnectedPlc.IsConnected);
-                object tsObj = await notConnectedPlc.ReadStructAsync<TestStruct>(DB2);
+                await Assert.ThrowsExceptionAsync<PlcException>(async () => await notConnectedPlc.ReadStructAsync<TestStruct>(DB2));
             }
         }
 
diff --git a/S7.Net/COTP.cs b/S7.Net/COTP.cs
index 7604c0d..8f60423 100644
--- a/S7.Net/COTP.cs
+++ b/S7.Net/COTP.cs
@@ -54,8 +54,11 @@ namespace S7.Net
             public static TPDU Read(Stream stream)
             {
                 var tpkt = TPKT.Read(stream);
-                if (tpkt.Length > 0) return new TPDU(tpkt);
-                return null;
+                if (tpkt.Length == 0)
+                {
+                    throw new TPDUInvalidException("No protocol data received");
+                }
+                return new TPDU(tpkt);
             }
 
             /// <summary>
@@ -67,8 +70,11 @@ namespace S7.Net
             public static async Task<TPDU> ReadAsync(Stream stream)
             {
                 var tpkt = await TPKT.ReadAsync(stream);
-                if (tpkt.Length > 0) return new TPDU(tpkt);
-                return null;
+                if (tpkt.Length == 0)
+                {
+                    throw new TPDUInvalidException("No protocol data received");
+                }
+                return new TPDU(tpkt);
             }
 
             public override string ToString()
@@ -98,7 +104,6 @@ namespace S7.Net
             public static byte[] Read(Stream stream)
             {
                 var segment = TPDU.Read(stream);
-                if (segment == null) return null;
 
                 var buffer = new byte[segment.Data.Length];
                 var output = new MemoryStream(buffer);
@@ -125,7 +130,6 @@ namespace S7.Net
             public static async Task<byte[]> ReadAsync(Stream stream)
             {                
                 var segment = await TPDU.ReadAsync(stream);
-                if (segment == null) return null;
 
                 var buffer = new byte[segment.Data.Length];
                 var output = new MemoryStream(buffer);
diff --git a/S7.Net/PLC.cs b/S7.Net/PLC.cs
index 8d98d4f..f11e568 100644
--- a/S7.Net/PLC.cs
+++ b/S7.Net/PLC.cs
@@ -15,8 +15,8 @@ namespace S7.Net
         private const int CONNECTION_TIMED_OUT_ERROR_CODE = 10060;
         
         //TCP connection to device
-        private TcpClient tcpClient;
-        private NetworkStream stream;
+        private TcpClient? tcpClient;
+        private NetworkStream? _stream;
 
         private int readTimeout = System.Threading.Timeout.Infinite;
         private int writeTimeout = System.Threading.Timeout.Infinite;
@@ -24,27 +24,27 @@ namespace S7.Net
         /// <summary>
         /// IP address of the PLC
         /// </summary>
-        public string IP { get; private set; }
+        public string IP { get; }
 
         /// <summary>
         /// PORT Number of the PLC, default is 102
         /// </summary>
-        public int Port { get; private set; }
+        public int Port { get; }
 
         /// <summary>
         /// CPU type of the PLC
         /// </summary>
-        public CpuType CPU { get; private set; }
+        public CpuType CPU { get; }
 
         /// <summary>
         /// Rack of the PLC
         /// </summary>
-        public Int16 Rack { get; private set; }
+        public Int16 Rack { get; }
 
         /// <summary>
         /// Slot of the CPU of the PLC
         /// </summary>
-        public Int16 Slot { get; private set; }
+        public Int16 Slot { get; }
 
         /// <summary>
         /// Max PDU size this cpu supports
diff --git a/S7.Net/PLCExceptions.cs b/S7.Net/PLCExceptions.cs
index c06823b..2b1034d 100644
--- a/S7.Net/PLCExceptions.cs
+++ b/S7.Net/PLCExceptions.cs
@@ -89,4 +89,25 @@ namespace S7.Net
         }
         #endif
     }
+
+    internal class TPDUInvalidException : Exception
+    {
+        public TPDUInvalidException() : base()
+        {
+        }
+
+        public TPDUInvalidException(string message) : base(message)
+        {
+        }
+
+        public TPDUInvalidException(string message, Exception innerException) : base(message, innerException)
+        {
+        }
+
+#if NET_FULL
+        protected TPDUInvalidException(SerializationInfo info, StreamingContext context) : base(info, context)
+        {
+        }
+#endif
+    }
 }
diff --git a/S7.Net/PLCHelpers.cs b/S7.Net/PLCHelpers.cs
index 602c6a6..2286264 100644
--- a/S7.Net/PLCHelpers.cs
+++ b/S7.Net/PLCHelpers.cs
@@ -82,7 +82,7 @@ namespace S7.Net
         /// <param name="varCount"></param>
         /// <param name="bitAdr"></param>
         /// <returns></returns>
-        private object ParseBytes(VarType varType, byte[] bytes, int varCount, byte bitAdr = 0)
+        private object? ParseBytes(VarType varType, byte[] bytes, int varCount, byte bitAdr = 0)
         {
             if (bytes == null || bytes.Length == 0)
                 return null;
diff --git a/S7.Net/PlcAsynchronous.cs b/S7.Net/PlcAsynchronous.cs
index 9e82c8d..601a3a4 100644
--- a/S7.Net/PlcAsynchronous.cs
+++ b/S7.Net/PlcAsynchronous.cs
@@ -5,6 +5,7 @@ using System.Linq;
 using System.Net.Sockets;
 using System.Threading.Tasks;
 using S7.Net.Protocol;
+using System.IO;
 
 namespace S7.Net
 {
@@ -20,9 +21,14 @@ namespace S7.Net
         public async Task OpenAsync()
         {
             await ConnectAsync();
+            var stream = GetStreamIfAvailable();
 
             await stream.WriteAsync(ConnectionRequest.GetCOTPConnectionRequest(CPU, Rack, Slot), 0, 22);
             var response = await COTP.TPDU.ReadAsync(stream);
+            if (response == null)
+            {
+                throw new Exception("Error reading Connection Confirm. Malformed TPDU packet");
+            }
             if (response.PDUType != 0xd0) //Connect Confirm
             {
                 throw new InvalidDataException("Error reading Connection Confirm", response.TPkt.Data, 1, 0x0d);
@@ -46,9 +52,10 @@ namespace S7.Net
             tcpClient = new TcpClient();
             ConfigureConnection();
             await tcpClient.ConnectAsync(IP, Port);
-            stream = tcpClient.GetStream();
+            _stream = tcpClient.GetStream();
         }
 
+
         /// <summary>
         /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
         /// If the read was not successful, check LastErrorCode or LastErrorString.
@@ -87,7 +94,7 @@ namespace S7.Net
         /// <param name="varType">Type of the variable/s that you are reading</param>
         /// <param name="bitAdr">Address of bit. If you want to read DB1.DBX200.6, set 6 to this parameter.</param>
         /// <param name="varCount"></param>
-        public async Task<object> ReadAsync(DataType dataType, int db, int startByteAdr, VarType varType, int varCount, byte bitAdr = 0)
+        public async Task<object?> ReadAsync(DataType dataType, int db, int startByteAdr, VarType varType, int varCount, byte bitAdr = 0)
         {
             int cntBytes = VarTypeToByteLength(varType, varCount);
             byte[] bytes = await ReadBytesAsync(dataType, db, startByteAdr, cntBytes);
@@ -100,7 +107,7 @@ namespace S7.Net
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
         /// <returns>Returns an object that contains the value. This object must be cast accordingly.</returns>
-        public async Task<object> ReadAsync(string variable)
+        public async Task<object?> ReadAsync(string variable)
         {
             var adr = new PLCAddress(variable);
             return await ReadAsync(adr.DataType, adr.DbNumber, adr.StartByte, adr.VarType, 1, (byte)adr.BitNumber);
@@ -113,7 +120,7 @@ namespace S7.Net
         /// <param name="db">Address of the DB.</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>Returns a struct that must be cast.</returns>
-        public async Task<object> ReadStructAsync(Type structType, int db, int startByteAdr = 0)
+        public async Task<object?> ReadStructAsync(Type structType, int db, int startByteAdr = 0)
         {
             int numBytes = Types.Struct.GetStructSize(structType);
             // now read the package
@@ -168,7 +175,7 @@ namespace S7.Net
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>An instance of the class with the values read from the PLC. If no data has been read, null will be returned</returns>
-        public async Task<T> ReadClassAsync<T>(int db, int startByteAdr = 0) where T : class
+        public async Task<T?> ReadClassAsync<T>(int db, int startByteAdr = 0) where T : class
         {
             return await ReadClassAsync(() => Activator.CreateInstance<T>(), db, startByteAdr);
         }
@@ -182,7 +189,7 @@ namespace S7.Net
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>An instance of the class with the values read from the PLC. If no data has been read, null will be returned</returns>
-        public async Task<T> ReadClassAsync<T>(Func<T> classFactory, int db, int startByteAdr = 0) where T : class
+        public async Task<T?> ReadClassAsync<T>(Func<T> classFactory, int db, int startByteAdr = 0) where T : class
         {
             var instance = classFactory();
             var res = await ReadClassAsync(instance, db, startByteAdr);
@@ -208,7 +215,9 @@ namespace S7.Net
             //Snap7 seems to choke on PDU sizes above 256 even if snap7 
             //replies with bigger PDU size in connection setup.
             AssertPduSizeForRead(dataItems);
-            
+
+            var stream = GetStreamIfAvailable();
+
             try
             {
                 // first create the header
@@ -376,6 +385,8 @@ namespace S7.Net
 
         private async Task<byte[]> ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, int count)
         {
+            var stream = GetStreamIfAvailable();
+
             byte[] bytes = new byte[count];
 
             // first create the header
@@ -406,6 +417,8 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
+            var stream = GetStreamIfAvailable();
+
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
             await stream.WriteAsync(message.Array, 0, length).ConfigureAwait(false);
@@ -424,6 +437,8 @@ namespace S7.Net
         /// <returns>A task that represents the asynchronous write operation.</returns>
         private async Task WriteBytesWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, byte[] value)
         {
+            var stream = GetStreamIfAvailable();
+
             byte[] bReceive = new byte[513];
             int varCount = 0;
 
@@ -469,6 +484,8 @@ namespace S7.Net
 
         private async Task WriteBitWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue)
         {
+            var stream = GetStreamIfAvailable();
+
             byte[] bReceive = new byte[513];
             int varCount = 0;
 
@@ -510,5 +527,14 @@ namespace S7.Net
                 throw new PlcException(ErrorCode.WriteData, exc);
             }
         }
+
+        private Stream GetStreamIfAvailable()
+        {
+            if (_stream == null)
+            {
+                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+            }
+            return _stream;
+        }
     }
 }
diff --git a/S7.Net/PlcSynchronous.cs b/S7.Net/PlcSynchronous.cs
index c101b3e..74b02bc 100644
--- a/S7.Net/PlcSynchronous.cs
+++ b/S7.Net/PlcSynchronous.cs
@@ -19,6 +19,7 @@ namespace S7.Net
 
             try
             {
+                var stream = GetStreamIfAvailable();
                 stream.Write(ConnectionRequest.GetCOTPConnectionRequest(CPU, Rack, Slot), 0, 22);
                 var response = COTP.TPDU.Read(stream);
                 if (response.PDUType != 0xd0) //Connect Confirm
@@ -52,7 +53,7 @@ namespace S7.Net
                 tcpClient = new TcpClient();
                 ConfigureConnection();
                 tcpClient.Connect(IP, Port);
-                stream = tcpClient.GetStream();
+                _stream = tcpClient.GetStream();
             }
             catch (SocketException sex)
             {
@@ -106,7 +107,7 @@ namespace S7.Net
         /// <param name="varType">Type of the variable/s that you are reading</param>
         /// <param name="bitAdr">Address of bit. If you want to read DB1.DBX200.6, set 6 to this parameter.</param>
         /// <param name="varCount"></param>
-        public object Read(DataType dataType, int db, int startByteAdr, VarType varType, int varCount, byte bitAdr = 0)
+        public object? Read(DataType dataType, int db, int startByteAdr, VarType varType, int varCount, byte bitAdr = 0)
         {
             int cntBytes = VarTypeToByteLength(varType, varCount);
             byte[] bytes = ReadBytes(dataType, db, startByteAdr, cntBytes);
@@ -119,8 +120,8 @@ namespace S7.Net
         /// If the read was not successful, check LastErrorCode or LastErrorString.
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
-        /// <returns>Returns an object that contains the value. This object must be cast accordingly.</returns>
-        public object Read(string variable)
+        /// <returns>Returns an object that contains the value. This object must be cast accordingly. If no data has been read, null will be returned</returns>
+        public object? Read(string variable)
         {
             var adr = new PLCAddress(variable);
             return Read(adr.DataType, adr.DbNumber, adr.StartByte, adr.VarType, 1, (byte)adr.BitNumber);
@@ -132,8 +133,8 @@ namespace S7.Net
         /// <param name="structType">Type of the struct to be readed (es.: TypeOf(MyStruct)).</param>
         /// <param name="db">Address of the DB.</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
-        /// <returns>Returns a struct that must be cast.</returns>
-        public object ReadStruct(Type structType, int db, int startByteAdr = 0)
+        /// <returns>Returns a struct that must be cast. If no data has been read, null will be returned</returns>
+        public object? ReadStruct(Type structType, int db, int startByteAdr = 0)
         {
             int numBytes = Struct.GetStructSize(structType);
             // now read the package
@@ -188,7 +189,7 @@ namespace S7.Net
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>An instance of the class with the values read from the PLC. If no data has been read, null will be returned</returns>
-        public T ReadClass<T>(int db, int startByteAdr = 0) where T : class
+        public T? ReadClass<T>(int db, int startByteAdr = 0) where T : class
         {
             return ReadClass(() => Activator.CreateInstance<T>(), db, startByteAdr);
         }
@@ -202,7 +203,7 @@ namespace S7.Net
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>An instance of the class with the values read from the PLC. If no data has been read, null will be returned</returns>
-        public T ReadClass<T>(Func<T> classFactory, int db, int startByteAdr = 0) where T : class
+        public T? ReadClass<T>(Func<T> classFactory, int db, int startByteAdr = 0) where T : class
         {
             var instance = classFactory();
             int readBytes = ReadClass(instance, db, startByteAdr);
@@ -340,6 +341,7 @@ namespace S7.Net
 
         private byte[] ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, int count)
         {
+            var stream = GetStreamIfAvailable();
             byte[] bytes = new byte[count];
             try
             {
@@ -375,6 +377,8 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
+            var stream = GetStreamIfAvailable();
+
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
             stream.Write(message.Array, 0, length);
@@ -385,6 +389,7 @@ namespace S7.Net
 
         private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, byte[] value)
         {
+            var stream = GetStreamIfAvailable();
             int varCount = 0;
             try
             {
@@ -429,6 +434,7 @@ namespace S7.Net
 
         private void WriteBitWithASingleRequest(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue)
         {
+            var stream = GetStreamIfAvailable();
             int varCount = 0;
 
             try
@@ -484,6 +490,8 @@ namespace S7.Net
             //replies with bigger PDU size in connection setup.
             AssertPduSizeForRead(dataItems);
 
+            var stream = GetStreamIfAvailable();
+
             try
             {
                 // first create the header
diff --git a/S7.Net/Protocol/S7WriteMultiple.cs b/S7.Net/Protocol/S7WriteMultiple.cs
index 2b92ef5..2738a34 100644
--- a/S7.Net/Protocol/S7WriteMultiple.cs
+++ b/S7.Net/Protocol/S7WriteMultiple.cs
@@ -91,7 +91,7 @@ namespace S7.Net.Protocol
 
             IList<byte> itemResults = new ArraySegment<byte>(message, 14, dataItems.Length);
 
-            List<Exception> errors = null;
+            List<Exception>? errors = null;
 
             for (int i = 0; i < dataItems.Length; i++)
             {
diff --git a/S7.Net/S7.Net.csproj b/S7.Net/S7.Net.csproj
index 007c374..94f659b 100644
--- a/S7.Net/S7.Net.csproj
+++ b/S7.Net/S7.Net.csproj
@@ -15,6 +15,8 @@
     <RepositoryType>git</RepositoryType>
     <PackageTags>PLC Siemens Communication S7</PackageTags>
     <Copyright>Derek Heiser 2015</Copyright>
+    <LangVersion>8.0</LangVersion>
+    <Nullable>Enable</Nullable>
     <DebugType>portable</DebugType>
     <EmbedAllSources>true</EmbedAllSources>
     <IncludeSymbols>true</IncludeSymbols>
diff --git a/S7.Net/TPKT.cs b/S7.Net/TPKT.cs
index a3af212..2b988d3 100644
--- a/S7.Net/TPKT.cs
+++ b/S7.Net/TPKT.cs
@@ -10,10 +10,19 @@ namespace S7.Net
     /// </summary>
     internal class TPKT
     {
+
+
         public byte Version;
         public byte Reserved1;
         public int Length;
         public byte[] Data;
+        private TPKT(byte version, byte reserved1, int length, byte[] data)
+        {
+            Version = version;
+            Reserved1 = reserved1;
+            Length = length;
+            Data = data;
+        }
 
         /// <summary>
         /// Reads a TPKT from the socket
@@ -24,21 +33,28 @@ namespace S7.Net
         {
             var buf = new byte[4];
             int len = stream.Read(buf, 0, 4);
-            if (len < 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
-            var pkt = new TPKT
+            if (len < 4) throw new TPKTInvalidException("TPKT header incomplete / invalid");
+            var version = buf[0];
+            var reserved1 = buf[1];
+            var length = buf[2] * 256 + buf[3]; //BigEndian
+
+            if (length == 0)
             {
-                Version = buf[0],
-                Reserved1 = buf[1],
-                Length = buf[2] * 256 + buf[3] //BigEndian
-            };
-            if (pkt.Length > 0)
-            {
-                pkt.Data = new byte[pkt.Length - 4];
-                len = stream.Read(pkt.Data, 0, pkt.Length - 4);
-                if (len < pkt.Length - 4)
-                    throw new TPKTInvalidException("TPKT is incomplete / invalid");
+                throw new TPKTInvalidException("TPKT payload length is zero");
             }
-            return pkt;
+
+            var data = new byte[length - 4];
+            len = stream.Read(data, 0, length - 4);
+            if (len < length - 4)
+                throw new TPKTInvalidException("TPKT payload incomplete / invalid");
+
+            return new TPKT
+            (
+                version: version,
+                reserved1: reserved1,
+                length: length,
+                data: data
+            );
         }
 
         /// <summary>
@@ -50,20 +66,28 @@ namespace S7.Net
         {
             var buf = new byte[4];
             int len = await stream.ReadAsync(buf, 0, 4);
-            if (len < 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
-            var pkt = new TPKT
+            if (len < 4) throw new TPKTInvalidException("TPKT header incomplete / invalid");
+            var version = buf[0];
+            var reserved1 = buf[1];
+            var length = buf[2] * 256 + buf[3]; //BigEndian
+
+            if (length == 0)
             {
-                Version = buf[0],
-                Reserved1 = buf[1],
-                Length = buf[2] * 256 + buf[3] //BigEndian
-            };
-            if (pkt.Length > 0)
-            {
-                pkt.Data = new byte[pkt.Length - 4];
-                len = await stream.ReadAsync(pkt.Data, 0, pkt.Length - 4);
-                if (len < pkt.Length - 4) throw new TPKTInvalidException("TPKT is incomplete / invalid");
+                throw new TPKTInvalidException("TPKT payload length is zero");
             }
-            return pkt;
+
+            var data = new byte[length - 4];
+            len = await stream.ReadAsync(data, 0, length - 4);
+            if (len < length - 4)
+                throw new TPKTInvalidException("TPKT payload incomplete / invalid");
+
+            return new TPKT
+            (
+                version: version,
+                reserved1: reserved1,
+                length: length,
+                data: data
+            );
         }
 
         public override string ToString()
diff --git a/S7.Net/Types/Class.cs b/S7.Net/Types/Class.cs
index 1052808..ab76f8d 100644
--- a/S7.Net/Types/Class.cs
+++ b/S7.Net/Types/Class.cs
@@ -106,9 +106,9 @@ namespace S7.Net.Types
             return numBytes;
         }
 
-        private static object GetPropertyValue(Type propertyType, byte[] bytes, ref double numBytes)
+        private static object? GetPropertyValue(Type propertyType, byte[] bytes, ref double numBytes)
         {
-            object value = null;
+            object? value = null;
 
             switch (propertyType.Name)
             {
@@ -245,7 +245,7 @@ namespace S7.Net.Types
         {
             int bytePos = 0;
             int bitPos = 0;
-            byte[] bytes2 = null;
+            byte[]? bytes2 = null;
 
             switch (propertyValue.GetType().Name)
             {
diff --git a/S7.Net/Types/DataItem.cs b/S7.Net/Types/DataItem.cs
index ca338c8..c944ffa 100644
--- a/S7.Net/Types/DataItem.cs
+++ b/S7.Net/Types/DataItem.cs
@@ -40,7 +40,7 @@ namespace S7.Net.Types
         /// <summary>
         /// Contains the value of the memory area after the read has been executed
         /// </summary>
-        public object Value { get; set; }
+        public object? Value { get; set; }
 
         /// <summary>
         /// Create an instance of DataItem
@@ -83,7 +83,14 @@ namespace S7.Net.Types
             var dataItem = FromAddress(address);
             dataItem.Value = value;
 
-            if (typeof(T).IsArray) dataItem.Count = ((Array) dataItem.Value).Length;
+            if (typeof(T).IsArray)
+            {
+                var array = ((Array?)dataItem.Value);
+                if ( array != null)
+                {
+                    dataItem.Count = array.Length;
+                }
+            }
 
             return dataItem;
         }
diff --git a/S7.Net/Types/Struct.cs b/S7.Net/Types/Struct.cs
index 3d569e5..733800a 100644
--- a/S7.Net/Types/Struct.cs
+++ b/S7.Net/Types/Struct.cs
@@ -70,7 +70,7 @@ namespace S7.Net.Types
         /// <param name="structType">The struct type</param>
         /// <param name="bytes">The array of bytes</param>
         /// <returns>The object depending on the struct type or null if fails(array-length != struct-length</returns>
-        public static object FromBytes(Type structType, byte[] bytes)
+        public static object? FromBytes(Type structType, byte[] bytes)
         {
             if (bytes == null)
                 return null;
@@ -198,7 +198,7 @@ namespace S7.Net.Types
 
             int size = Struct.GetStructSize(type);
             byte[] bytes = new byte[size];
-            byte[] bytes2 = null;
+            byte[]? bytes2 = null;
 
             int bytePos = 0;
             int bitPos = 0;