diff --git a/S7.Net/Protocol/Serialization.cs b/S7.Net/Protocol/Serialization.cs
index 3ecee55..b9ac9a5 100644
--- a/S7.Net/Protocol/Serialization.cs
+++ b/S7.Net/Protocol/Serialization.cs
@@ -13,6 +13,10 @@ namespace S7.Net.Protocol
 
         public static byte[] SerializeDataItem(DataItem dataItem)
         {
+            if (dataItem.Value == null)
+            {
+                throw new Exception($"DataItem.Value is null, cannot serialize. StartAddr={dataItem.StartByteAdr} VarType={dataItem.VarType}");
+            }
             if (dataItem.Value is string s)
                 return dataItem.VarType == VarType.StringEx
                     ? StringEx.ToByteArray(s, dataItem.Count)
diff --git a/S7.Net/Types/TypeHelper.cs b/S7.Net/Types/TypeHelper.cs
index 983299b..af5441b 100644
--- a/S7.Net/Types/TypeHelper.cs
+++ b/S7.Net/Types/TypeHelper.cs
@@ -24,7 +24,7 @@ namespace S7.Net.Types
         /// <summary>
         /// Converts an array of T repesented as S7 binary data to an array of T
         /// </summary>
-        public static T[] ToArray<T>(byte[] bytes, Func<byte[], T> converter)
+        public static T[] ToArray<T>(byte[] bytes, Func<byte[], T> converter) where T : struct
         {
             var typeSize = Marshal.SizeOf(default(T));
             var entries = bytes.Length / typeSize;