This lambda does not compile, but I do not understand why.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using LinqKit;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
    {
        var barModel = new BarModel();
        string id = "some";

        Console.WriteLine(barModel.subFor(id).ToString());
            // output: m => (True AndAlso (m.key == value(ConsoleApplication2.Bar`1+<>c__DisplayClass0[ConsoleApplication2.Model]).id))
        Console.ReadKey();


        var subworkitems = barModel.list.Where(barModel.subFor(id).Compile());
                // Exception {"variable 'm' of type 'ConsoleApplication2.Model' referenced from scope '', but it is not defined"}

        Console.WriteLine(subworkitems.ToString());
        Console.ReadKey();
    }
}

class Bar<TModel>
{

    public Bar(Expression<Func<TModel, string>> foreignKeyExpression)
    {
        _foreignKeyExpression = foreignKeyExpression;
    }

    private Expression<Func<TModel, string>> _foreignKeyExpression { get; set; }

    public Expression<Func<TModel, bool>> subFor(string id)
    {

        var ex = forTargetId(id);

        return ex;
    }

    public Expression<Func<TModel, bool>> forTargetId(String id)
    {

        var fc = _foreignKeyExpression;

        Expression<Func<TModel, bool>> predicate = m => true;

        var result = predicate.And(m => fc.Invoke(m) == id).Expand();

        return result;

    }

}

class Model
{
    public string key;
    public string value;
}

class BarModel : Bar<Model>
{
    public List<Model> list;

    public BarModel() : base(m => m.key) 
    {
        list = new List<Model>();
    }
}


}