Merge #207 into latest master

Dapper NET40/SqlMapper.cs

@@ -2795,6 +2795,8 @@ public static void PackListParameters(IDbCommand command, string namePrefix, obj
                 bool isString = value is IEnumerable<string>;
                 bool isDbString = value is IEnumerable<DbString>;
                 DbType dbType = 0;
+                if (list != null)
+                {
                     foreach (var item in list)
                     {
                         if (count++ == 0)
@@ -2807,7 +2809,7 @@ public static void PackListParameters(IDbCommand command, string namePrefix, obj
                         if (isString)
                         {
                             listParam.Size = DbString.DefaultLength;
-                        if (item != null && ((string)item).Length > DbString.DefaultLength)
+                            if (item != null && ((string) item).Length > DbString.DefaultLength)
                             {
                                 listParam.Size = -1;
                             }
@@ -2827,6 +2829,7 @@ public static void PackListParameters(IDbCommand command, string namePrefix, obj
                             command.Parameters.Add(listParam);
                         }
                     }
+                }
 
                 var regexIncludingUnknown = @"([?@:]" + Regex.Escape(namePrefix) + @")(?!\w)(\s+(?i)unknown(?-i))?";
                 if (count == 0)