about lambdas

[Michael]

R  With(I, R)(I o, R function (I) fun)
{
	static if(isAssignable!(I, typeof(null)))
		return o is null ? null : fun(o);
	else
		return fun(o);
}

class Person
{
	private
	{
		string  _name;
		Address _address;
	}

	@property
	{
		string name() { return	_name; }
		void   name(string v) { _name = v; }

		Address address() { return _address; }
		void	address(Address v) { _address = v; }
	}
}

in main function
----------------
foreach(p; persons)	
	p.With((Person x) => x.address); // works

but
----------------
foreach(p; persons)	
		p.With(x => x.address); // error

nullcheck.d(89): Error: template maybe.With does not match any 
function template
  declaration. Candidates are:
maybe.d(20):        maybe.With(I, R)(I o, R function(I) fun)
nullcheck.d(89): Error: template maybe.With(I, R)(I o, R 
function(I) fun) cannot
  deduce template function from argument types !()(Person,void)


Why?