Why the compiler adds an extra parameter for delegates when there is no closure?

Question

I was playing with delegates and noticed that when I create a Func<int,int,int> like the example below:

Func<int, int, int> func1 = (x, y) => x * y; 

The signature of the compiler generated method is not what I expected:

As you can see it takes an object for it's first parameter. But when there is a closure:

int z = 10; Func<int, int, int> func1 = (x, y) => x * y * z; 

Everything works as expected:

This is the IL code for the method with extra parameter:

    .method private hidebysig static int32  '<Main>b__0'(object A_0,                                                      int32 x,                                                      int32 y) cil managed {   .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 )    // Code size       8 (0x8)   .maxstack  2   .locals init ([0] int32 V_0)   IL_0000:  ldarg.1   IL_0001:  ldarg.2   IL_0002:  mul   IL_0003:  stloc.0   IL_0004:  br.s       IL_0006   IL_0006:  ldloc.0   IL_0007:  ret } // end of method Program::'<Main>b__0' 

It seems that the parameter A_0 is not even used. So, what is the purpose of the object parameter in the first case? Why isn't it added when there is a closure?

Note: If you have a better idea for the title please feel free to edit.

Note 2: I compiled the first code in both Debug and Release modes, there was no difference. But I compiled second in Debug mode to get a closure behaviour since it optimizes the local variable in Release mode.

Note 3: I'm using Visual Studio 2014 CTP.

Edit: This is the generated code for Main in the first case:

.method private hidebysig static void  Main(string[] args) cil managed {   .entrypoint   // Code size       30 (0x1e)   .maxstack  2   .locals init ([0] class [mscorlib]System.Func`3<int32,int32,int32> func1)   IL_0000:  nop   IL_0001:  ldsfld     class [mscorlib]System.Func`3<int32,int32,int32> ConsoleApplication9.Program::'CS$<>9__CachedAnonymousMethodDelegate1'   IL_0006:  dup   IL_0007:  brtrue.s   IL_001c   IL_0009:  pop   IL_000a:  ldnull   IL_000b:  ldftn      int32 ConsoleApplication9.Program::'<Main>b__0'(object,                                                                        int32,                                                                        int32)   IL_0011:  newobj     instance void class [mscorlib]System.Func`3<int32,int32,int32>::.ctor(object,                                                                                              native int)   IL_0016:  dup   IL_0017:  stsfld     class [mscorlib]System.Func`3<int32,int32,int32> ConsoleApplication9.Program::'CS$<>9__CachedAnonymousMethodDelegate1'   IL_001c:  stloc.0   IL_001d:  ret } // end of method Program::Main