Make Nick happy, better error for constructorless types

Dapper/SqlMapper.cs

@@ -1504,7 +1504,12 @@ static List<FieldInfo> GetSettableFields(Type t)
             }
             else
             {
-                il.Emit(OpCodes.Newobj, type.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, Type.EmptyTypes, null));
+                var ctor = type.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, Type.EmptyTypes, null); 
+                if (ctor == null) 
+                {
+                    throw new InvalidOperationException("A parameterless default constructor is required to allow for dapper materialization");
+                }
+                il.Emit(OpCodes.Newobj, ctor);
                 il.Emit(OpCodes.Stloc_1);
             }
             il.BeginExceptionBlock();

Tests/Tests.cs

@@ -33,6 +33,29 @@ public class ConcreteOrder : Order
             }
         }
 
+        class NoDefualtConstructor 
+        {
+            public NoDefualtConstructor(int a)
+            {
+                A = a;
+            }
+            public int A { get; set; }
+        }
+
+        public void EnsureNoConstructorGivesNiceError()
+        {
+            try
+            {
+                connection.Query<NoDefualtConstructor>("select 1 A").First();
+            }
+            catch(InvalidOperationException e)
+            {
+                e.Message.IsEqualTo("A parameterless default constructor is required to allow for dapper materialization");
+            }
+   
+        }
+
+
         // http://stackoverflow.com/q/8593871
         public void TestAbstractInheritance() 
         {
@@ -42,10 +65,8 @@ public void TestAbstractInheritance()
             order.ProtectedVal.IsEqualTo(2);
             order.Public.IsEqualTo(3);
             order.Concrete.IsEqualTo(4);
-            
         }
 
-
         public void TestListOfAnsiStrings()
         {
             var results = connection.Query<string>("select * from (select 'a' str union select 'b' union select 'c') X where str in @strings",